OIL MEDIA

 DRYING OILS are fatty oils of vegetable matter that can react chem­ ically with the oxygen in the air eventually to solidify and become dry

to the touch.  Nondrying  oils are mineral  oils and vegetable oils, such  as peanut oil and cottonseed oil, that  resemble  animal  fats  and,  because they do not oxidize naturally and harden, are unsuitable as a binder for paint.

Resins are either natural or synthetic organic chemicals that are sol­ ids or viscous (thick) liquids. They are used  to make  media for paint­ ing (they are often too brittle when used alone) to alter the working characteristic of the paint film. Resins, in a liquid form, differ from drying oils because they solidify by the ,evaporation of their solvent rather than through oxidation. Drying oils thicken and harden into a  paint  film over a two-to five­ day period, while most dissolved resins thicken and harden within hours.

Paint that is taken directly from the tube usually needs to be "let down," or thinned to a workable consistency. No ts' paint should ever be let down with only a thinner such as turpentine. This w hes away the drying oil that  coats each particle of pigment and protects a pigmen'tfrom interacting chemically with other pigments. The drying oil also holds the pigments together as a paint film; therefore, the less you have, the weaker the paint film. Most of  the  cost  in  making an oil paint is in the meticulous care taken in coating each particle of pigment.

As early as A.D. ll00, Theophilus, a German monk, wrote about the use of a drying oil as a medium for painting. The slow drying rate of  the oils prevented their immediate acceptance, but after it was discovered that the  addition of  zinc and lead to the oil reduced the drying time, painting with oil  became  wide­  spread. The practice of using oils, which imparted smoothness to a painted sur­ face, was introduced around 1390 in Italy and the  Netherlands.  With  the  beginning of the age of industrialization (from the eighteenth through the nine­ teenth centuries), knowledge of earlier materials and  methods  fell  into  a  dark age. This was not because of deliberate secrecy, but because of disuse and the demise of the apprenticeship system, in which a student worked directly with a master to learn the craft. Much  vital information  about specific  drying  times of oil media and their use in causing paint films to interlock for durability has been lost.

 

DRYING OILS

DRYING OIL is both the binder and  the  vehicle for  the  pigments  that are used  in oil painting. Each particle of pigment must be thoroughly coated  with  oil  to protect it from reacting chemically with other pigment particles, to allow proper dispersion of pigment particles for luminosity, and to provide a workable and durable paint film. It is important to understand that drying  oils  do  not  dry through evaporation, but through oxidation, which  is  a  chemical  reaction  with the oxygen in the air. Painters  often ask,  "Why  must I wait six months  to a year to varnish paintings when they seem dry to the touch?" The answer is that if oxidation is not complete below as well as on  the surface  of  the paint  film  and the surface is sealed off from its supply of oxygen, the still-wet paint is trapped underneath and proper drying is prevented.

LINSEED OILS

Linseed oil is made from flax seeds, which  contain  30 to 40 percent  oil.  It dries to the touch quickly, between three and ten days,  but  it  takes  years  before  it dries completely. It tends to yellow  with  age  because  of  the  linolenic  acid, which is one of its binding agents (the other is  linoleic  acid).  A  refinement process is commonly used during the manufacture of linseed oil to remove par­ ticulate matter and mucilage and to bleach out some of the yellow color.

Raw Commercial Linseed Oil is extracted from  flax seeds  today  by crushing and steaming procedures developed in the nineteenth century. The better com­ mercial grades are warmed and aged to remove the grossest particles.  Raw lin­ seed oil is the least desirable for use in any artists'  paints or even  commercial  paint products because it contains the greatest  amount  of  mucilage  and impurities. It is perfectly acceptable for finishing raw wood furniture.

Refined Linseed Oil is most commonly made by steaming the crushed flax seeds and chemically bleaching the oil. The bleaching has only a temporary effect and  the oil usually reverts to its original yellow color. There are many  grades  of linseed oil; the artist grade is often further treated with  alkali  to improve clarity and color, producing a pure oil that is pale, clear, and thin. Paint is produced by grinding raw pigment in the oil. Additional refined linseed oil is often added to prepared paint to thin the paint, and to  add  gloss  and  transparency.  It  is also used to slow the drying time of the paint film. If the oil is used sparingly, the paint film dries in approximately three days. Drying can take ten or more days  if the oil is used more generously.

Cold-Pressed Linseed Oil is the best of the linseed oils. It is produced from the first pressing of ripe linseeds. It is the least efficient method of producing large amounts of linseed oil, but it gives rise to the purest form. Because  of  its high  cost, it is rarely used in making paints. It is expensive because it  is  produced  solely for artists' use by the least efficient method. This oil resists embrittlement, has excellent flow characteristics, and adds  gloss and  transparency  to a  paint.  It is used to thin paint and it allows brush strokes to level out of a paint film. Cold-pressed linseed oil is a slower drying oil than refined linseed oil.

Stand Oil was widely used in the Dutch school of painting during the seven­ teenth century. This oil is so called because of the old practice of letting the oil stand for long periods of  time to allow  the impurities  to settle out. Today,  stand oil is linseed oil that has been heated  without air  at a temperature  between  525 and 575°F. This polymerizes the oil, making it viscous and thereby excellent for glazing and leveling brush strokes. Because it is a fatter oil, it is  not  recom­ mended for underpainting, but rather for the top paint  layers.  It  makes  a  paint film that is not only tougher, but also yellows less than regular linseed oil. The drying time for stand oil is slower than that of linseed oil.

Sun-Thickened Linseed Oil is made by placing partially covered linseed oil in the sun. This bleaches, slightly polymerizes, and partially oxidizes the oil, pro­ ducing an oil that has characteristics somewhere between refined linseed oil and stand oil. It dries a little faster than both (between  two and  nine days,  depending on the thickness applied). It dries more quickly than  refined  linseed  oil because the oxidation process has already begun. This could, however, result in a less durable paint film.

 

POPPY OIL

Extracted from poppy seeds, poppy oil is slower drying-usually five days-than linseed oil. (Some companies, including Winsor & Newton, add cobalt driers to accelerate the drying time.) This oil, which is less  yellow  in  appearance  than other oils because it does not contain linolenic acid (one of  the  two  binding  agents in oil paint films, and the one that yellows more), is used in making or mixing the pale oil colors.  But  because  it  does not contain  linolenic  acid,  there is a greater risk of cracking with paint films composed primarily of poppy oil. Consequently, it should not be the primary ingredient in a  painting  medium recipe.

 

SAFFLOWER OIL AND SUNFLOWER OIL

Safflower oil and sunflower oil have come into use only recently. They are presently used by :some manufacturers m; :sub:slilules for linseed oil when making some of the paler colors. They are also used in the manufacture of alkyd resins. Although at this time it appears that both sunflower and safflower  oil  can  be safely used in the manufacture  of  some colors,  they  are  not recommended for use in media and are not expected to replace linseed oil.

 

Driers, or Siccatives

DRIERS, or siccatives, are usually metallic salts that are combined  with  oils or resins and then mixed into the paint and/or medium and/or  varnish  to accelerate the drying time by speeding the rate of oxidation and polymerization. But it is important to remember that driers diminish the life of the paint or varnish. With good judgment and experience, however, they can be used safely. The following guidelines may prove helpful.

l. Use a drier only in glazes or in thinly painted pictures.

  1. Never use more than 3 percent concentrate to media consisting primarily of a drying oil, and 6 percent to oil-resin media combinations.

  2. Never apply a faster-drying paint film over a wet, slower-drying paint film.

  3. Test a drier before use on something other than your final picture.

Cobalt drier, siccative de Courtrai (primarily lead linoleate), and siccative de Haarlem (primarily damar resin) are among the more common driers. Cobalt and damar are the least harmful because they work primarily while the paint is in a liquid state, their action becoming progressively less as the paint  film  hardens. This is not the case with lead driers, which  can continue  to act  even  after  the paint film hardens. Siccative de Haarlem is safer than siccative  de  Courtrai because of its lower lead content and proportionately larger amount  of  damar resin. Similar drying effects can be obtained by mixing small amounts of faster­ drying colors into slower-drying colors, for example, mixing cobalt, manganese, viridian, and lead-containing colors with slower-drying colors  such  as  phthalo blue or lamp black.

 

RESINS

Resins are added to painting  media  primarily for three reasons.  First, a mixture  of drying oil and resin will offer a paint film that can  be worked  over  within  hours or, at maximum, the next day because when the solvent evaporates, which happens within several hours, the resin hardens, holding the drying oil in place  until it can oxidize and solidify.  Second,  a resin  may  be u ed  to dilute  a  paint for glazing without overthinning it. If a glaze is too watery, it will run uncon­ trollably over the painting surface. Finally, resins dry with greater clarity than drying oils and they will add brilliance to paint films.

Resins are also the primary material used for varnishing paintings.  Today, the five most com­ monly used resins are copal, damar, mastic, Venice turpentine, and alkyd.

COPAL

Copal is a hard resin. Originally, the copal used in painting media was the fossil resin amber. Now that amber is considered a semiprecious stone and has become virtually unavailable to the artist, the copal  available for  artists'  use is unspec­ ified tree-root resins. There are many grades available on the  world  market and  the best are rarely used for making media. In addition to thickening a paint  medium, adding leveling properties to the paint film, and increasing gloss,  this resin also exhibits a thixotropic effect (see page 257), which is particularly  helpful in glazing.

Copal is a hard resin which can only be liquified through  heating  with  a  solvent and so, when  it dries,  it is difficult  to dissolve  unless it is reheated.  This is a desirable characteristic because if a protective  varnish  such  as damar  has to be removed to clean or restore a painting, this can easily be done  without  great  risk of dissolving underlying paint films which contain the copal resin. This insolubility at room temperature also means that a copal varnish makes an excel­ lent isolating varnish (see page 269) when applying successive glazes.

The disadvantage of copal is that it darkens with age.  Although  the  actual reason for this darkening is not known,  it is speculated  that it is due to changes  that occur during the heating necessary  to dissolve  the resin.  Copal is brittle and  is best used conservatively with a flexible drying oil like stand  oil. The  differ­ ence between a "copal medium" and a "copal varnish" is that the varnish often contains driers, which add to the risk of  cracking,  and  therefore  the  varnish  is not best used in making a painting medium. Today, many of  the commercially made copal media have no copal at all and are composed  of synthetic  substitutes or alkyd resins. These substitutes are safer  to use as a medium,  being less  brit­  tle, but they should not be used to replace copal varnish.

DAMAR

Damar is collected from the fir tree genus Shorea or from Hopea trees of  South­ east Asia. Damar is a soft resin and is readily dissolved in turpentine (not  in mineral spirits, because it is then partially insoluble) at room  temperature  and is the most popular additive to a painting medium  as  well as the most commonly used resin for varnishing.  Damar when used in painting  media helps  paint films  to set up quickly so that they may be worked over within a day. It is possible to interlock paint layers by taking advantage of the two types of  drying that occur with a damar-drying oil combination. Several hours after using this combination, the damar has hardened and the drying oil has begun to polymerize through oxidation. If, in one and a half to two days, when  the drying  oil is roughly  half dry. a second paint layer containing the same medium is applied,  the two layers will interlock. The turpentine of the medium when applied will redissolve part of the resin and soften the drying oil of the paint film  underneath,  and  the  two should lock together. This process can be used to produce beautiful and subtle effects. Damar also adds gloss and brilliance to a painting.

MASTIC

Mastic is an exudate from the Mediterranean mastic shrub Pistazia lentiscus, also known as the pistachia tree. Like damar, it is a soft resin totally soluble  in turpentine and only partially soluble in mineral spirits. The use of mastic resin in painting dates back to the time of Rembrandt and the Dutch Masters and is responsible for Rembrandt's blue backgrounds now appearing  green.  This is due  to the yellowing of the mastic he used in the application of five or six coats of varnish. Mastic is still popular today primarily as an ingredient  for  media  (see page 264) rather than as a varnish. The yellowing effect of mastic is less pro­ nounced when it is used in a medium and many painters feel its advantages outweigh this drawback. One of the advantages is that a mastic  solution  dries faster than all the resin solutions-one  hour  in its pure fom1.  It also dries clearer and with more gloss than damar. Many people who use mastic use it in com­ bination with damar, fifty/fifty in a recipe calling for one or the other. This ratio reduces the yellowing of the mastic and helps to speed the drying of the damar.

 

VENICE TURPENTINE

Genuine Venice turpentine is collected from larch trees. It is a viscous liquid resin; such resins exude from certain trees and are often referred to as balsams. Venice turpentine has been used in painting for centuries and has excellent han­ dling and aging characteristics. It should not be confused with the thinners gum turpentine or rectified turpentine. Venice turpentine is used as an additive to thkken other  media.  This  resin  is  popular  because  it  gives  body  to  the  paint  film while maintaining gloss and brilliance, and it yellows very little over time. Gen­ uine Venice turpentine is not easily found and some companies are using a sub­ stitute resin called Canada balsam. Canada balsam has two advantages over Venice turpentine-it dries more clearly and it takes only one or two hours to dry, as opposed to three days for Venice turpentine. However, Canada balsam has a distinct disadvantage in that it is more fluid than Venice turpentine.

 
OIL-MODIFIED ALKYD RESIN

Alkyd resin is the category of resins that are  made  from  mixtures  of  dibasic acids and polyhydric alcohols. There are many alkyd resins and each  manufac­ turer picks a favorite and keeps it a secret. The quality and concentration of an alkyd resin or medium can vary a great deal from manufacturer to manufacturer. The selected resin is chemically combined with a nonyellowing oil, such as safflower oil, producing a workable,  fast-drying  medium.  Most  manufacturers add driers to speed up the drying time and silica to give extra body.

Alkyd resins can exhibit a thixotropic effect. Thixotropy is an unusual phe­ nomenon where a gel or paste suddenly loses its plasticity when disturbed  or moved mechanically, resulting iri a liquid. The opposite may also occur where a liquid, left undisturbed, forms into a gel. This effect can be used to advantage during glazing by helping to prevent the glaze  from  spreading  uncontrollably  over the painted surface. However, this characteristic is undesirable with impasto techniques. Alkyd resins should not be overthinned, so add no more  than  25 percent thinner to resin.

COPAL

Copal is a hard resin. Originally, the copal used in painting media was the fossil resin amber. Now that amber is considered a semiprecious stone and has become virtually unavailable to the artist, the copal  available for  artists'  use is unspec­ ified tree-root resins. There are many grades available on the  world  market and  the best are rarely used for making media. In addition to thickening a paint  medium, adding leveling properties to the paint film, and increasing gloss,  this resin also exhibits a thixotropic effect (see page 257), which is particularly  help­ful in glazing.

Copal is a hard resin which can only be liquified through  heating  with  a  solvent and so, when  it dries,  it is difficult  to dissolve  unless it is reheated.  This is a desirable characteristic because if a protective  varnish  such  as damar  has to be removed to clean or restore a painting, this can easily be done  without  great  risk of dissolving underlying paint films which contain the copal resin. This insolubility at room temperature also means that a copal varnish makes an excel­ lent isolating varnish (see page 269) when applying successive glazes.

The disadvantage of copal is that it darkens with age.  Although  the  actual reason for this darkening is not known,  it is speculated  that it is due to changes  that occur during the heating necessary  to dissolve  the resin.  Copal is brittle and  is best used conservatively with a flexible drying oil like stand  oil. The  differ­ ence between a "copal medium" and a "copal varnish" is that the varnish often contains driers, which add to the risk of  cracking,  and  therefore  the  varnish  is not best used in making a painting medium. Today, many of  the commercially made copal media have no copal at all and are composed  of synthetic  substitutes or alkyd resins. These substitutes are safer  to use as a medium,  being less  brit­  tle, but they should not be used to replace copal varnish.

DAMAR

Damar is collected from the fir tree genus Shorea or from Hopea trees of  South­ east Asia. Damar is a soft resin and is readily dissolved in turpentine (not  in mineral spirits, because it is then partially insoluble) at room  temperature  and is the most popular additive to a painting medium  as  well as the most commonly used resin for varnishing.  Damar when used in painting  media helps  paint films  to set up quickly so that they may be worked over within a day. It is possible to interlock paint layers by taking advantage of the two types of  drying that occur with a damar-drying oil combination. Several hours after using this combination, the damar has hardened and the drying oil has begun to polymerize through oxidation. If, in one and a half to two days, when  the drying  oil is roughly  half dry. a second paint layer containing the same medium is applied,  the two layers will interlock. The turpentine of the medium when applied will redissolve part of the resin and soften the drying oil of the paint film  underneath,  and  the  two should lock together. This process can be used to produce beautiful and subtle effects. Damar also adds gloss and brilliance to a painting.

MASTIC

Mastic is an exudate from the Mediterranean mastic shrub Pistazia lentiscus, also known as the pistachia tree. Like damar, it is a soft resin totally soluble  in turpentine and only partially soluble in mineral spirits. The use of mastic resin in painting dates back to the time of Rembrandt and the Dutch Masters and is responsible for Rembrandt's blue backgrounds now appearing  green.  This is due  to the yellowing of the mastic he used in the application of five or six coats of varnish. Mastic is still popular today primarily as an ingredient  for  media  (see page 264) rather than as a varnish. The yellowing effect of mastic is less pro­ nounced when it is used in a medium and many painters feel its advantages outweigh this drawback. One of the advantages is that a mastic  solution  dries faster than all the resin solutions-one  hour  in its pure fom1.  It also dries clearer and with more gloss than damar. Many people who use mastic use it in com­ bination with damar, fifty/fifty in a recipe calling for one or the other. This ratio reduces the yellowing of the mastic and helps to speed the drying of the damar.

 

VENICE TURPENTINE

Genuine Venice turpentine is collected from larch trees. It is a viscous liquid resin; such resins exude from certain trees and are often referred to as balsams. Venice turpentine has been used in painting for centuries and has excellent han­ dling and aging characteristics. It should not be confused with the thinners gum turpentine or rectified turpentine. Venice turpentine is used as an additive to thkken other  media.  This  resin  is  popular  because  it  gives  body  to  the  paint  film while maintaining gloss and brilliance, and it yellows very little over time. Gen­ uine Venice turpentine is not easily found and some companies are using a sub­ stitute resin called Canada balsam. Canada balsam has two advantages over Venice turpentine-it dries more clearly and it takes only one or two hours to dry, as opposed to three days for Venice turpentine. However, Canada balsam has a distinct disadvantage in that it is more fluid than Venice turpentine.

 

OIL-MODIFIED ALKYD RESIN

Alkyd resin is the category of resins that are  made  from  mixtures  of  dibasic acids and polyhydric alcohols. There are many alkyd resins and each  manufac­ turer picks a favorite and keeps it a secret. The quality and concentration of an alkyd resin or medium can vary a great deal from manufacturer to manufacturer. The selected resin is chemically combined with a nonyellowing oil, such as safflower oil, producing a workable,  fast-drying  medium.  Most  manufacturers add driers to speed up the drying time and silica to give extra body.

Alkyd resins can exhibit a thixotropic effect. Thixotropy is an unusual phe­ nomenon where a gel or paste suddenly loses its plasticity when disturbed  or moved mechanically, resulting iri a liquid. The opposite may also occur where a liquid, left undisturbed, forms into a gel. This effect can be used to advantage during glazing by helping to prevent the glaze  from  spreading  uncontrollably  over the painted surface. However, this characteristic is undesirable with impasto techniques. Alkyd resins should not be overthinned, so add no more  than  25 percent thinner to resin.

Waxes

Was as a base for a painting medium since the first century B.c. and remained popular until about A.D. 700. Today, there has been a resurgence in the use of various waxes in painting.  These  include  fossil  waxes,  paraffin  waxes, and beeswax. The use of such waxes in  painting  is  called  encaustics,  or encaustic painting. The term "encaustic" is derived from the Greek,  meaning "burnt in," which occurs after the painting is completed. This process involves heating the surface to remove all brush or knife marks and  to fuse  the  painting into one solid paint film. Tradition not withstanding, this final burning process is rarely used today. The best surviving examples of  early  encaustic  are  the mummy portraits from the Egyptian district of al-Fayyum from the first century B.C. A recent use of encaustic in painting is the Target and Flag paintings  by  Jasper Johns (c.1955). In these paintings, the pigmented beeswax was applied in translucent layers over strips of newspaper clippings.

The primary advantage of using beeswax, which must be kept warm during application, is that the surface can be worked over as soon as the  beeswax­ pigment mixture cools to room temperature. Since the wax can be softened and dissolved in turpentine or mineral spirits, an encaustic painting can be reworked with a brush and thinner.

Fossil waxes are actually far more commonly used today than the more expen­ sive beeswax. The great advantage to fossil waxes  is  that  they  do  not  require heat to make them pliable. Dorlands Wax Medium is  made  commercially  of fossil wax, which can be mixed directly with oil paint. It is ready to use with or without heat and is relatively inexpensive. It hardens as the solvent evaporates, which takes several times longer than cooling beeswax.  Beeswax,  despite  its great expense, the difficulty of finding it in a pure and  bleached  state,  and  its  need to be heated, is still preferred for heavy impasto technique.

Wax media set up quickly, drying to the touch within thirty minutes, although final curing is quite slow.  A  wax-medium  paint film  will dry with a matte sheen. If desired, a semigloss appearance can be created by polishing the heated  and cooled surface with a silk cloth. Surface quality has become an important con­ sideration for many contemporary artists, who feel that surface reflection detracts from the direct experience of their work. The major  disadvantage  in the  use of wax is the danger of melting when it  is exposed  to  high  temperatures.  If  you wish to retain the matte quality, remember that this can easily  be  lost  if  the surface is polished by improper handling.

 

Media

Whenever a paint is thinned it should always be thinned with a medium, of which the simplest form is a combination  of  thinner  and drying oil. The amount of thinner used should be less than 50 percent of the recipe because there will always be sufficient drying oil replacing whatever might be washed away by the thinner.

A medium is chosen not just to thin a paint, but also to alter its working characteristics, drying time, and final appearance. Resins, waxes, and driers are used as additives to basic thinner-drying oil media to make these changes. No matter what formula is used to create a medium, the principle of fat over  lean should never be violated in its application. ("Fat" means  a  medium  rich  in oil  and "lean" refers to a medium rich in thinner. A lean medium or paint mixture should never be applied over a fat one.)

Most of the following recipes have been offered by artists who  have  had  success using them. Some are from previously published literature  to  which  I have made small changes, primarily to update them for currently available mate­ rials. I would like to thank  all  those  who laid  the groundwork  for these recipes by their courageous experimentation with different materials on their own work.

 

SIMPLE MEDIA

 

The following diagram describes two distinctly different media. The drying oil­ turpentine medium is for thinning  paint mixtures and the wax-turpentine medium is for thickening paint mixtures.

DIAGRAM OF SIMPLE MEDIA

 

Drying  Oil  or Wax

(linseed oil, poppy oil, stand oil, or wax)

Thinner

(turpentine, petroleum distillate)

A few drops of drier may be added  to speed  the drying time if wax is not used.

 

 

Drying Oil-Turpentine Medium. A drying oil-turpentine medium is the most common type of medium used. It is the simplest to make and many paint manu­ facturers sell it premixed.  It consists of 60 percent drying oil,  usually linseed  oil  or stand oil, and 40 percent turpentine. The percentage of turpentine should be reduced as layers of paint are built up over one another.

The disadvantage of this method is the increased drying time as the thinner is reduced and the oil is increased  in  the fat over  lean  process.  Turpentine-drying oil media also have no body and tend to run down  the  canvas,  especially  in glazes. (A glaze is a paint that has been thinned greatly  with  a  medium  to disperse the pigments in the  paint. This makes the  paint  transparent  and allows the application of a thin veil  of  color over another.) The drying time  of  this type of medium is slow, from two to five days, unless mixed with driers or  a fast­  drying color like manganese blue.

Wax-Turpentine Medium. A wax-turpentine medium may be heated and used with oil paint or mixed with dry pigment. It is ideal for impasto  technique.  The wax should be warmed in a double boiler reserved for just this purpose and dry pigment may be added directly. (Keep in mind that dry pigment is difficult to handle safely and can be extremely dangerous.)

WAX-TURPENTINE MEDIUM

 1 part wax (preferably  beeswax) 3 parts rectified turpentine

Warm in a double boiler and stir until the wax is dissolved. Pour into a wide-mouth container.

May be worked over in 30 minutes.

INTERMEDIATE MEDIA

 

The following recipes are easy to prepare and provide greater versatility  than simple media.

DIAGRAM OF INTERMEDIATE MEDIA

 

Drying  Oil

I

Thinner

(If natural resin is involved use only genuine turpentine.)

I

Resin  or Wax

(damar solution, damar varnish, Venice  turpentine,  or wax)  A few drops of drier may be added.

 

 

Copal-Drying Oil Medium. Copal media are ideal for producing very hard and durable, although brittle, paint films that can be applied without softening or redissolving previous paint layers. This allows for an  egg-temperalike  effect where one color can be painted over another after it has dried without the two colors mixing.

 

1 part copal varnish 
1 part genuine turpentine

1 part linseed oil (Stand oil may be substituted. The drying oil reduces the brittleness of the copal resin.)

 

The drying rate is approximately two hours if the copal varnish used contains driers;
if it does not contain  driers, the drying time will be approximately  1½  days.
  (Please note that this means workably dry, not totally dry.)

 

 

Damar-Drying Oil Medium. The difference between this medium and that of  the copal-drying oil medium is that the damar will soften and partially redissolve when successive layers of paint mixed with this medium are applied.  This  allows the two paint films to interlock and to appear less isolated  from  each  other. Damar also yellows and darkens much less than copal. It is  also  less  brittle. Damar is not as hard a resin as copal and is therefore less durable, but not sufficiently so to cause concern. The following recipe also has better leveling properties than a copal medium.

 

1 part damar varnish (Damar heavy gum solution may be substituted for extra thick body.)

1 part stand oil

to 5 parts rectified turpentine

(This proportion may also be varied for desired fat or lean quality.)

15 drops of cobalt  drier may  be added  to every  8 ounces of  medium to speed drying.

The drying time is between 2 and 3 days (without the drier).

Stand Oil-Venice Turpentine Medium. The combination of stand oil and Venice turpentine will give a thick, resinous medium with enamellike  leveling  proper­ ties. Glazes with this medium will be exceptionally clear and brilliant.

1 part stand oil

3 parts Venice turpentine 0 to 3 parts turpentine

(Vary turpentine according to fat over lean principles.)

 

It is necessary to warm the stand oil and Venice turpentine first to make mixing them easier.

Paint films using the formula  can often  be  worked  over in 1 to 2 days.

Greater brilliance as well as a shorter time between application of paint films can be had by adding some damar heavy gum solution (this is a concentrated form, which can be bought or made).

 

 

COMPLEX MEDIA

 

The following media are significantly more difficult  to  prepare,  yet are  among the most versatile.

DIAGRAM OF COMPLEX MEDIA

 

Drying  Oil I

Thinner

(If natural resins are involved use only genuine turpentine.)

I

Resin  A

(i.e.,  damar varnish)

I

Resin  B

(mastic solution, Venice  turpentine,  or wax) A few drops of drier may be used.

 

Damar-Oil-Venice Turpentine Medium. This is ideal as an all-purpose painting medium. If you use less turpentine,  it is excellent  for  glazing.  Both  the damar and Venice turpentine allow for the interlocking of successive layers of paint.

 

 

DAMAR-OIL-VENICE TURPENTINE MEDIUM

 

9 parts damar varnish (to add gloss, increase  brilliance, and speed drying)

4 parts stand oil (to aid leveling and to give body)

2 parts Venice turpentine (This is  a resin  and  its  purpose is
to thicken the medium and add brilliance.)

4 to 9 parts rectified turpentine (To comply with fat over lean, the amount of turpentine should
be reduced to  4 parts in successive layers. Do not substitute another thinner.)

Without the addition of  a drier,  this  medium  will often be ready to work over in 24 hours. A small amount  of drier can speed this up.

Linseed Oil-Mastic Media. The combination of linseed oil and mastic, called megilp, was popular in the eighteenth and nineteenth centuries as a painting medium, although it is now blamed for many of the disastrous effects seen in paintings of this period. At first, the mastic resin was thought responsible for the cracking, blistering, and browning that occurred.  It  is  now  thought,  however,  that these undesirable affects were caused primarily  by  the extended  heating  of the mastic resin called for in the recipe and by the excessive use of driers in combination with impure turpentine.  Megilp  was so popular  because it appeared to dry, in some cases, in only fifteen minutes, and in several hours in heavier applications. It reportedly had a wide range of handling properties and was excellent for impasto and glazing. There has been a resurgence of  interest  in linseed oil-mastic combinations, and various "improved" formulas have evolved. The resurgence started in the 1930s; however, fifty years is not enough time to make an unequivocable recommendation one way or the other. Time is the only known test for such media as these. There are many  variations of  megilp  reci­  pes, none of which I feel sufficiently confident about to offer at this time.

Flemish medium is an example of an all-purpose painting medium made with mastic and oil that has been handed down through time. It has excellent handling characteristics, and the mastic creates a brilliantly clear paint film. The following recipe is used today with excellent results. The ingredients  are similar  to those used to make the infamous megilp; however, there are several important differ­ ences regarding heat, turpentine, and the use of driers-the  mastic  is  not  added until the end of heating, only rectified turpentine  is  used,  and  the  amount  of drier is small.

FLEMISH  MEDIUM

 

20 parts linseed oil (cold-pressed preferable) 14 parts rectified turpentine

7 parts mastic tears, or crystals

1 part litharge (lead monoxide-This is  highly  poisonous  and  is  not sold in art supply stores;
it must be obtained  through  chemical supply houses. If pale drying oil, which is made with  litharge, 
is used instead of linseed oil, then this ingredient is unnecessary.)

 

Mix the poisonous litharge in a small amount of oil,  using  a palette knife, until a paste is formed. (This will prevent the litharge from set­ tling to the bottom of the cooking pot when it is later added.) The remaining oil should  be heated outdoors or with proper ventilation  over a low flame in a covered enamel cooking pan. The pan  should  hold twice the volume of the ingredients. An  asbestos  mat placed  between the flame and the pan will reduce the possibility of scorching.

When the mixture is warm, approximately 320°F, or 160°C, add the litharge. Gradually increase the temperature, over 2½ hours,  with  the last 30 minutes at exactly 482°F, or 250°C. Stir occasionally with a wooden spoon.

Allow the medium to cool to 392°F, or 200°C, by placing the pan on a stack of old newspapers and then stirring and fanning.

Now add the mastic in small amounts, stirring constantly. The medium will foam up as you add the mastic; if stirring is constant the foam will rapidly dissipate.

Next, very slowly add the cold turpentine.  The  medium  will  again foam up; this will dissipate if stirred and fanned.

Pour the warm medium, approximately 284°F, or 140°C, into a wide­ mouth container and allow it to cool before covering.

Beeswax and Oil. This combination was used by Rubens because of its extreme versatility. It could be effective in impasto or as a glaze, but the disadvantage  is that it is a dark medium and tends to discolor all colors. The following is a traditional recipe which has been updated.

 

BEESWAX AND OIL MEDIUM

  IO parts linseed  oil (cold-pressed  preferable) 2 parts beeswax

1/8 part litharge (lead monoxide--This is  highly  poisonous  and  must be obtained from a chemical supply  house. 
However,  this ingredient can be omitted if pale drying oil is substituted for the linseed oil.)

 

Mix the poisonous litharge in a small amount of oil, using a palette knife, until a paste is formed. (This will prevent the litharge  from settling to the bottom of the cooking pan when added later.) The remaining oil should be heated outdoors or with  proper  ventilation, over a low flame in a covered enamel cooking pan. The  pan should  hold twice the volume of the ingredients. An asbestos mat placed between the flame and the pan  will  reduce  the  possibility  of scorching. When the mixture  is  wann,  approximately 320°F, or 160°C, add the litharge and broken pieces of beeswax. Gradually increase the temperature over 2½ hours, with the last 30 minutes at exactly 482°F, or 250°C. Stir occasionally with a wooden spoon.

When the mixture  appears black with brown fumes  rising, it is ready. Allow the medium to cool; do  not refrigerate  or place  the  hot pan on a cold surface (a stack  of  old  newspapers  works  well).  Pour the cooled medium, approximately 284°F, or  140°C,  into a wide­ mouth container and allow it to cool before covering.

 

COMMERCIALLY PREPARED MEDIA

Commercially prepared media have a narrow range. They are primarily simple media, although occasionally intermediate and complex media can be found. Among the most commonly offered commercial painting media is a mixture of stand oil and turpentine, which usually carries a brand name. That such media as these continue to sell, and  sell in quantity,  testifies  to either  incredible  laziness  or a profound lack of understanding of these materials.  With  the exception  of these  media,  many of the other painting  media offered  by manufacturers  can  be a justifiable convenience. In fact, most other commercial  media consist either of  all or part of some version of an oil-modified alkyd resin, which would be impossible to prepare at home. The use of alkyd as well as other synthetic resins  has become so widespread that they have all but replaced many of the traditional ingredients used in Commercially prepared media.

Prepared media such as Liquin by Winsor  &  Newton,  Zee  by  Grumbacher, and Res-n-gel by the Weber Company, are some examples of primarily oil-modi­ fied-alkyd resins. The pastelike quality found in  some  of  these  media  is often due to the addition of silica. Grumbacher's Gel is  designed  to  give  body  to a paint mixture necessarily speeding the drying time. Liquin behaves similarly to a copal-drying oil medium and, in fact, similar formulations have  been  suc­  cessfully offered by other manufacturers as a substitute for this medium.  LeFranc & Bourgeois offers a ready-made Flemish Medium, based upon mastic and thickened oil with oxides,  which  has the consistency  of  a gel and  which is sold in tubes. It also produces a medium it calls Venetian Medium, which is a ready­ made wax-oil medium prepared similarly to its Flemish Medium,  except  that a hard wax is used rather than  mastic.  This  medium  could  be a viable alternative to preparing the beeswax and oil medium previously described.

The only serious caution I would add about thinning prepared media that con­ tain alkyd resins is that these resins are sensitive to overthinning and can break down chemically. I recommend that you use no more than 25 percent thinner to prepared media. So far, over the past ten years, these new prepared media have demonstrated great flexibility and durability whether applied thickly or thinly.

Diluents, or Solvents

SOLVENTS ARE USED in painting primarily  to  thm  the  pamt  or  meamm,  ana should then evaporate from the paint film without leaving a trace. The next most important function of thinners such as turpentine is to clean tools and  brushes. Keep these two principles in mind as you read the following descriptions of the various solvents.

Many thinners and solvents can be hazardous to health. They are not  only inhaled and ingested, but are absorbed directly through the skin.

Gum Turpentine is made from distilling the resinous gum from pine trees. Gum turpentine usually contains a small amount of sticky residue, which can  be imparted to a painting if this kind of  turpentine  is  used  in  large  quantities.  It may remain in the layers of paint, inhibiting proper drying and, in time, causing discoloration. Unless cost is a serious consideration, I do not recommend  using gum turpentine with artist-grade paints and media. It is, however, perfectly acceptable for cleaning tools and brushes.

Rectified, or Artist-Grade, Turpentine is double distilled  to remove the last bit of residue from the pine-tree gum. This thinner is ideal for oil paints and media because it does the job and then evaporates from the paint film without a trace. Artists often buy the finest paints and media and then use the cheapest thinners. This is like buying a Rolls Royce and putting kerosene in the gas tank. There are areas where compromises can be made, but they should be made with common sense.

Venice Turpentine is a resin used as a thickening agent in the preparation of media. Petroleum Distillate, Mineral Spirits, and  White Spirits are byproducts  from the manufacture and refinement of petroleum. Although they are all basically the same type of product, the actual chemical composition may differ vastly from  brand to brand. This is of little concern when purchasing a product  made  for artists' paint such as a turpentine substitute. There can be a serious problem, however, if this solvent is used with house paints or if house paint mineral spirit thinners are used with artists' materials. Always test a solvent with a  particular paint no matter what the label says. 

The advantage of using  petroleum  distillates  that are produced  for artistic  use is that they are less expensive than turpentine, have a longer shelf life, leave no sticky residue, and according to government standards, are less hazardous than turpentine. They are also recommended for painters who are allergic  to  turpen­ tine. There are, however, two drawbacks. The first is that demar and mastic are partially insoluble in these solvents. The other is that they have a decidedly oily smell, which some people may find offensive.

Odorless Paint Thinners are essentially the same as petroleum distillate or min­ eral spirits except that the unpleasant odor has been removed or masked.  All are fine turpentine substitutes if you avoid using them with damar or mastic.

Remember, however, that the paint thinner  that  is sold  in  hardware  stores is not the same, and may contain other solvents that can  destroy  an  artist-grade paint, ruin brushes, substantially increase health  risks,  or cause  other  dangerous or unpredictable results. One artist reports that she was using a paint thinner purchased at a hardware store, when all of a sudden  the hairs  were falling out of her brushes in clumps. She had been using hardware-store paint thinner without serious problems until this incident. After investigation, it was discovered  that many of the solvents packaged for hardware stores under the  name  "paint thin­ ner" may be changed by the manufacturer without notice. These changes may be perfectly satisfactory for hardware use, but in this case the last batch of paint  thinner the artist purchased was,  unfortunately,  particularly  good  at  dissolving the glues used to hold her brushes together.

Oil Spike of Lavender is one of the oldest  known  turpentine  substitutes.  It is the essential oil from the lavender plant and possesses a most wonderful scent. It evaporates more slowly than turpentine,  is nonflammable,  and  is primarily  used as a turpentine substitute by those who are allergic to turpentine.  Since  it  is  slower drying than turpentine, it is occasionally  used  to slow  the drying  time of oil paint. Its disadvantages are its extremely high cost and limited availability. Currently, the only sources of this product are Winsor & Newton, Sennelier, and Schmincke.

 

Varnishes

VARNISH IS RESIN dissolved in turpentine or in a  mixture  of  turpentine  and  a drying oil such as linseed oil. There are several resins available with  which  to make a varnish, and the selection of a resin is guided by use.

Picture Varnish is used as a final coating for a painting to protect the picture and unify the appearance of the surface. It can, for example, make the surface appear  either  matte  or  shiny,  or  protect   the   paint   film   from   chemical   reactions  with the atmosphere and from mechanical abrasion.

Retouch Varnish is used to give a full and wet look to the surface of the  unfinished painting before work is resumed. This prevents the eye from being fooled by the unevenness of the light reflected from  parts  of  the  painting's surface.

Mixing Varnish is used as an additive to the painting medium to accelerate the drying time, to add gloss, and to give body to a glaze.

Isolating Varnish is a resin that is insoluble in turpentine  or  mineral  spirits. When this varnish is applied to a paint film, it will protect  it from  being affected by the turpentine or mineral spirits in the next layer of paint to be applied.

 

TYPES OF VARNISHES

The following are descriptions of various types of varnishes and their uses. Commercially prepared varnishes are readily available, or varnish can be made from recipes given in this section. 

Damar Varnish is the most popular of all varnishes and is used as a retouch, a mixing, and a picture varnish. It does not bloom (develop a chalky  appearance)  and it yellows less than most natural resins. Damar varnish can be readily pur­ chased already prepared or you can prepare it according to the following recipe.

 

DAMAR VARNISH

1 part crushed damar resin wrapped in muslin

4 parts rectified turpentine

Leave wrapped resin to soak in the rectified turpentine for 1 or. 2 days, or until the resin has dissolved.

Filter if necessary.

Dries in approximately 1 hour.

 

 

Mastic Varnish is clearer than damar and can be applied  more easily.  However, it does tend to bloom (develop a chalky surface) in humid climates, as well as yellow more than damar. Mastic and mastic varnishes are much more expensive and harder to come by than damar. Today, mastic is usually used as a mixing varnish and rarely as a picture varnish. A mastic solution (concentrate) for paint­ ing as well as a varnish can be prepared from the following recipe.

 

MASTIC SOLUTION

(from which the varnish is made)

 

1 part mastic tears (The  better  mastic  comes  in  the form of tears, or little round balls.)

3 parts rectified turpentine (The best turpentine should be used, especially if the varnish will be used in painting.)

The preparation of mastic solution is sensitive to impurities and heat. The mastic tears should not be crushed to  speed  the  process.  The tears should be suspended in a gauze bag or nylon stocking and allowed to dissolve without use of heat. This takes 1 or 2 days.

Mastic has a more stable shelf life as a solution (heavy gum solution is best) than as a varnish. Therefore, you may wish to consider diluting a mastic solution to make the varnish. This  may  be done  by  adding 1  part rectified turpentine to 3 parts mastic solution.

Mastic varnish will dry in 1 hour.

 

Copal Varnish and copal medium are becoming increasingly difficult to find because amber has become semiprecious and rare. It is being replaced by such synthetics as alkyds or unspecified tree-root resins.

Copal varnish makes an excellent isolating varnish, when used in moderation, and a very hard-surface final varnish. However, copal varnish is more often produced as a convenient source of liquid copal for use in media than as a final protective varnish. Since it has been found that copal varnish darkens and often cracks with age, even without the driers that are commonly added,  most recipes call for the use of stand oil or sun-thickened oil  to reduce  the risk  of  cracking. The following is a recipe for copal-oil varnish.

COPAL-OIL  VARNISH

 

  1. parts dry copal resin

  2. parts stand oil or sun-thickened oil

 

The oil should be heated to approximately 482°F, or 250°C, for 45 minutes to 1 hour. A sign of readiness  is  the  darkening  of  the  oil. Heat copal resin separately  until  it  melts  (between  356° and  644"F, or 180° and 340° C). Then slowly add the hot oil,  stirring  with  a wooden spoon. Allow the medium to cool, then store in wide-mouth bottles.

 

Shellac  is a resin gathered  from  the lac insect, Laccifer lacca. The  best shellac is called "true orange shellac," and it is not dyed to look orange. Shellac is insoluble in turpentine, but is soluble in alcohol.  It dries to a  hard,  tough,  flexi­ ble film when applied to something other than the surface of a painting.  On paintings it tends to crack and to darken  with age.  It can  be useful  as a sizing or an isolating varnish between paint layers (especially egg tempera).  It  is also a good, cheap fixative for charcoal and other drawings. It dries in about thirty minutes.

Synthetic Varnishes are, in most cases, composed of ketone or acrylic resins dissolved in mineral spirits. The advantages are that they dry rapidly, are crystal clear (unless a wax is added to create a matte finish), and are nonyellowing. The disadvantage is that, with the exception of polycyclohexanone, they can be used only as a picture varnish.

Polycyclohexanone is a synthetic damarlike resin, developed recently in Ger­ many,  that can be used alone or in conjunction  with damar for media or varnish.   It is prepared in the same way as damar. The advantage is  that  it  is optically clearer than, and yellows less than, damar. It also forms a  harder  and  more durable paint film. However, it is slightly more brittle than damar and, conse­ quently, is often used with other, more flexible resins. The  polycyclohexanone  adds clarity, and resins like damar add flexibility.

Soluvar is a synthetic varnish composed  of  acrylic  resin  produced  by Binney & Smith Company, which is available in both matte and  gloss.  It is  used  as a final, protective picture varnish on both oil paintings and acrylic paintings. It is receiving greater recognition because it can easily be  removed  if  the  picture needs to be cleaned or restored.

Matte Varnishes are made by adding to a varnish a flattening agent, which is usually a wax (such as beeswax or a fossil wax) or a waxlike substance such as aluminum stearate. Winsor & Newton's wax varnish and Dorland's Wax Medium are thick and are applied by rubbing the medium onto the surface of the painting and polishing it with a soft brush or silk cloth when dry. Liquid  matte  varnishes are made by suspending a wax in a varnish. The application  of  this  kind  of varnish is facilitated by warming the varnish until the cloudiness disappears and then applying it with either a soft brush or a warmed airbrush.

The advantage of a matte varnish is that there  is no surface  glare to interfere with viewing artwork. This has become an important consideration for many contemporary abstract artists. A slight sheen can give the illusion of a secondary color where there is none. This is less of a consideration in figurative  artwork where there are usually many variations in color and shape, which help to cam­ ouflage the shiny spots on the surface.

The disadvantages of matte varnish are that too much can leave a milky or  cloudy appearance on the surface, which is also easily damaged by rubbing.

 

APPLICATION OF VARNISHES

When applying varnish, the first consideration is whether the painting is really dry. Although a painting may feel dry to the touch within days or weeks,  the  layers below the surface may not be thoroughly dry. A paint film dries by react­ing with the oxygen in the air. If a painting is varnished before this reaction is completed in the paint layers below the surface, these paint layers are sealed off from their source of oxygen and cannot complete their drying process. The paint­ ing may remain soft and sticky for a considerable length of time and, with  improper drying, the paint film may not bond properly to other  film  layers. Another problem caused by premature varnishing is that the solvent of  the  var­ nish may penetrate the paint layers that are not completely dry,  thus softening them and affecting the appearance as well as the stability of the paint films.

Most paintings of average thickness and painted with a lean medium will be ready for varnishing between six months and a year after  completion.  Unless driers were used throughout the painting, one year is usually  the safest  choice when in doubt. If the paint is thick,  one  year  will  not  be long enough.  Never heat or place a painting in the sun to accelerate the  drying  process.  Because drying of oil paint is a chemical reaction with oxygen, rather than evaporation, rushing the process can cause wrinkling and other horrors. It is best to store the painting where there is light,  ventilation,  warmth, low humidity, and loving care.

Paintings that must be displayed before they are thoroughly dry can be shown either unvarnished or coated with a retquch varnish, which will even the surface appearance and will provide some protection. It  will also slow the ultimate dry­  ing time, but will not prevent proper oxidation.

During the lengthy drying process, the surface of the painting may collect ctust or dirt, which must be removed before varnishing.  Any  cleaning  must  not  involve the use of water because the water can penetrate the paint layers, thus reaching the ground and causing it to swell. This will weaken  the bond between the ground and the paint and can result in serious cracking. The best  way  to remove dust is first with a feather duster or a pigeon wing. Then  take a loaf  of fresh bread and pull out the center, squeeze it into a ball, and roll this over the surface of the painting. If there are slight grease stains, they may be removed by blotting with mineral spirits. If there are problems beyond those described here, professional advice is preferable to experimentation.

When the painting is dry, has a clean surface, and is in a dust-free, dry, warm environment, the varnish can be applied. The  two  basic methods of  application are spraying and brushing. Spray varnishing can be successful when applied to a surface that has a minimum of texture, but a spray cannot cover textural irregularities as well as a brush. If a spray is held too close to the surface, the  application will be too heavy and  may  run or pool. If  the  spray  is too far from the surface, some of the particles of spray may partially dry  en  route  to  the surface and give it a frosted or powdered look. If you begin to spray  off  the surface and then move evenly onto the surface, pooling can be avoided on the surface because the areas where you start, stop, or change direction will be outside the painted area. Two thin coats are superior to one thick coat.

For textured and irregular surfaces, brush application of varnish is best. The varnish can  be worked  into areas that are not easily  accessible  with a spray.  For a heavily textured surface, a hog or bristle brush  is necessary  to force the var nish into difficult areas. Ox hair is excellent for smoother surfaces.

After the application of the varnish, the painting should be laid flat to dry  for one or two days. The surface should be protected from falling particles and dust. This may be accomplished by laying a board over some books or strips of wood placed on opposite sides of the painting. This will bridge the painting and  will  keep the protective covering a few inches off the surface.

The contents of this site were previously published in "ART HARDWARE" by Steven Saitzyk 1987, © COPYRIGHT