The first step in discussing any paper board is to define a board. A paper-board is defined by its thickness. Any paper that is 0.012 inch or more, which is a little less than 1/64 inch in thickness, can accurately be called a board. Tissue paper is approximately 0.001 inch thick, bond paper ranges from 0.003 to 0.004 inch, and one-ply museum board ranges from 0.0125 to 0.015 inch. The material most commonly used to store and protect fine art is four-ply museum board and its thickness ranges from 0.050 to 0.060 inch (0.060 inch is almost 1/16th of an inch.)
At one time there were several ways to define various boards by their thickness. A standard mat board was said to be fourteen-ply (roughly the equivalent of putting together fourteen sheets of bond paper) and double-weight mat board twenty-eight-ply. A standard museum board, which is approximately equal to a mat board in thickness, is called four-ply because each ply is much thicker than bond paper and it takes only four to reach the desired thickness. Today, most manufacturers of paper boards are shifting toward using a point system of measurement, which will make it easier to comprehend thickness and to compare various boards. In the point system, one point equals 0.001 inch. Therefore, if the average mat board or museum board is between 0.050 and 0.060 inch it would be between 50 pt. and 60 pt. in thickness.
There can often be as much as a four-point variance of thickness within a manufacturer's advertised thickness. Manufacturers of mat board have, for the most part, dropped their system of defining thickness by plys in favor of the point system. Some manufacturers who make both mat board and boards for illustration, as well as for graphic arts, refer to their 50 pt. to 60 pt. boards as single weight, and their 100 pt. to 120 pt. boards as double weight. Museum boards are still most commonly referred to in plys, although the point system is rapidly taking over.
The type of board is defined by its content, such as ground-wood boards, which, regardless of whether or not the surface is rag, are for graphic art use or other non-fine artwork. Boards that can be used in archives, such as museum board, are composed of rag, cotton, or purified cellulose. In the case of foam centered boards, the center is composed of styrene. In the following entries there are explanations of the composition of the various boards and the reasons they are made the way they are, as well as indications of the circumstances under which they can be used with fine artwork.
A nonarchival board is made of unrefined or partially refined wood pulp, or from recycled paper products where the residual lignin content is greater than in cotton (1 to 2 percent). The term "nonarchival boards" also includes any board that cannot maintain a neutral or slightly alkaline pH, as well as any board with significant levels of metals like iron and copper, which can oxidize and stain. Boards that have colorant that can bleed, or that have an alum sizing, are also nonarchival.
In general, nonarchival boards are not safe as a permanent support for fine artwork, although some painters have had limited success in preparing such boards for fine artwork by coating both sides with an acrylic polymer before painting.
CARDBOARDS OR GROUND-WOOD BOARDS
This group of boards, which includes cardboards, chipboards, and upson boards, is made primarily from recycled paper products and ground wood. These boards are highly acidic and contain metals and petroleum products. They should not be used in the production, or the storage, of fine artwork.
Corrugated Cardboard that is ¼ inch, or single weight (called single wall in the cardboard trade), is composed of three sheets of a heavy, chemically treated, ground-wood pulp paper commonly called Kraft paper (named after the Kraft, or sulfate, pulp process). Two of the sheets are separated and the third, which is in the middle, is formed in a corrugated shape. This type of board has great strength in one direction. It is weak when bent along the corrugation, which can be compensated for by gluing two sheets of corrugated board together with the corrugation running in opposite directions. This results in an inexpensive and lightweight packing material.
Double-weight, or double-wall, corrugated board consists of five sheets of Kraft paper, two outside, one center, and two corrugated. Although the double weight is considerably stronger than single weight, it is still vulnerable to bending along the direction of the corrugation.
The strength of corrugated board depends on the thickness of the Kraft paper used to manufacture it. The type of corrugated board most commonly found in art supply stores is the same used to make the average corrugated cardboard box. It is single weight and is 36" x 72".
Henri de Toulouse-Lautrec often used corrugated cardboard for his artwork, and today it is not uncommon for people to follow his example. However, the limited number of surviving pieces produced on this board have only endured because of extensive conservation and restoration, not because this is a viable support for artwork. This board should not be used in contact with fine artwork or in conservation framing.
Chipboard and Newsboard are names that are used interchangeably. This type of board is made primarily of recycled paper products and, consequently, con tains a great variety of undesirable impurities from metal to petroleum products. This board is used as an inexpensive mounting and backing board in nonconser vation framing. It is often oil-impregnated; mounting, therefore, can be difficult and is often impermanent.
The appearance of chipboard ranges from an uneven brown to a mottled gray. The single weight is 45 to 55 pt., and double and triple weights are commonly available in the size 32" X40" and can be found in 40" X60".
Stencil Board is also produced by the Kraft (sulfate) paper-pulp process and is impregnated with oil or wax to make it waterproof. This waterproof quality keeps the board from absorbing the water of a waterborne paint and buckling. It also prevents the paint from flowing under the edge of the stenciled image. This board is, however, totally unsuitable as a ground for fine artwork. Most stencil boards are just thick enough to qualify as boards (12 pt.). The sizes most com monly available are 18" X 24" and 24" X 36".
COATED, OR COVERED, GROUND-WOOD BOARDS
Mat boards, illustration boards, mounting boards, Upson board, and watercolor board are among the ground-wood, or recycled paper, boards that have a surface covering that is designed to meet specific needs. Some of these boards can be used interchangeably, such as mat boards and mounting boards, but none of them should be used in the production of fine artwork or its storage.
Upsonite®, which is commonly referred to as Upson board, is produced by Domatar Industries, Inc. Although Upsonite is made largely from the same mate rials as chipboard, it is lower in density and a bit lighter in weight. It is also available in a greater variety of thickness, size, and surface. It ranges from 1/8 to 3/8 inch in thickness (the point system is not used for this board because it is treated more as a building material for temporary displays than as an art mate rial), and from 4' X 8' to 4' X12' in size. Textured finishes are produced in peb ble, smooth, and linen, as well as a waterproof variety for outdoor displays.
This board is used in the arts primarily for model buildings, such as sculptural or architectural models, and mounting photomurals. It is popular for theater sets, parade floats, and game boards.
Mounting Boards are chipboard covered with white paper. Inexpensive mount ing boards are covered on both sides with a clay-coated paper and are intended to be used only for mounting, such as for dry mounting photos and posters.
The better grades of mounting board are covered on one side with a bond paper, or inexpensive drawing paper, which is durable enough to handle pencil and paste-up. This type of mounting board is often referred to as mechanical, paste-up, or graphic arts board. It is designed to be an intermediate step in quality between boards that work well only in mounting, such as the clay-coated boards, and an illustration board, which is designed for multimedia. Graphic arts studios and newspaper publishers use this board for layouts, pasteups, and for the overall design of a project that will be reproduced by some printing process. Mechanical board is less expensive than illustration board, and its use can result in considerable savings, particularly when the board is used in large quantities. Conventional clay-coated boards do not work well with pen, marker, or pencil and will not stand up under the constant repositioning of material attached with rubber cement or wax.
Mechanical boards are widely available in single thickness, but double thickness boards can also be found. Mounting boards are available in white and gray. Single weight is between 45 pt. and 55 pt., and double and triple weights are common. Common sizes are 30" X 40", 32" X 40", and 40" X 60", though sizes like 20" X30" and 22" X28" are available in some of the better grades.·
Railroad Board is made from recycled paper and is clay-coated, or surfaced with white paper. This board is often made water resistant, to prevent buckling when waterborne paint is used or because of handling with wet hands. It is relatively thin as boards go, and its thickness is rated in terms of plys rather than points. The most common thickness, four-ply, is not standard, and it can range from 15 pt. to 20 pt. Also fairly common is six-ply, but virtually the only size it comes in is 22" X 28". The surface paper, which covers both sides of the recycled paper core, is only slightly refined. Railroad board is produced in white, black, and several lacklustre, dyed colors.
Poster Board is a thicker and slightly stiffer form of railroad board; six-ply and eight-ply are the common thicknesses. In addition to the 22" x 28" railroad size, poster board is available in 28" x 44". Poster board is covered only on one side with either white or colored paper. This board is used for show cards, picket signs, and display advertising.
Scratch Board is poster board covered with a white clay coating and a black-ink surface, which can be easily scraped away with a razor blade or a knife specially made for this purpose. When the surface coating is scraped away, the contrasting white clay layer is exposed. Art done on scratch board can resemble an etching or a woodblock print. This board is used primarily in the graphic arts to create images to be reproduced in various print media. Scratch board suffered in popularity in recent years and is no longer readily available.
Mat Boards are ground-wood boards with facings of decorative paper, metal foil, fabric, and simulated fabric, and as well as various textured finishes. The ground wood used in better-quality mat boards is from pulp where the tree bark and knots have been removed or at least avoided. Such impurities do not bleach or readily break down during processing and can show up in the bevel when a picture mat is cut. The reddish-brown appearance of particles from the knots can be a stark contrast to the bleached ground-wood bevel, making the mat a total loss.
Mat boards are used for decorative and display purposes in and out of a picture frame. Mats were originally developed to keep paper artwork from coming in contact with the glass inside a picture frame. Later, mats were further developed to add a decorative border to paper artwork. Because of the high acidity of most mat board, paper artwork often develops a brown stain when in close or direct contact with these boards. A yellow stain can develop in as little as six months on some of the more absorbent print papers use in fine artwork. After several years of contact, it is often quite noticeable on the surface of artwork near the exposed bevel of the mat. Today, the Crescent Cardboard Company has begun to try to remedy the formation of this brown stain by adding chemical buffers, such as calcium carbonate, to their boards. Accelerated aging tests per formed on their mat boards show that the boards still have a pH of 7.3 after a simulated one hundred years. It began with a pH of 7.7, so the increase in acidity would be considered negligible. Despite the good showing in pH this board should not be considered a substitute for museum board. It is only a much needed improvement of the standard ground-wood mat board. It is also likely that distributors of this board, as well as art supply stores and picture framers, will take several years to turn over their inventories for all the new boards. Using buffers is merely a temporary solution that will only delay the problem because the buffer will eventually be exhausted as the ground wood ages and as the boards absorb atmospheric pollutants.
The most common size of mat board is 32" x 40" with a thickness ranging from 55 to 60 pt. Selected colors are available in boards of 40" X48".
Illustration Boards are made of ground wood and have drawing paper adhered to one side. If the paper is smooth, like a plate-finish bristol, it is called hot press; if it has some texture, it is called cold press. Watercolor boards are illustration boards that have either a rough drawing paper or a thin watercolor paper surface. Acrylic boards have a canvas-like textured paper. Linen texture and laid finish (a charcoal or pastel paper finish) are available with in white, gray, and colored surfaces.
These boards are designed to be used for production art where surface appearance and convenience are the only requirements. The rigidity of the board's backing keeps the paper surface flat during and after use so that artwork will photograph without distortion. In addition, this kind of artwork often passes through many hands and, if it were not on board, it could easily be damaged. Fine artists have often recognized this convenience and have been fooled by terms like "100 percent rag surface" into believing that such boards are safe for fine artwork, particularly since it is not unusual to find high-quality paper used for the surface of an illustration and watercolor board. However, with the one exception of the Strathmore 100 percent rag illustration board, this refers only to the surface. The ground-wood backing makes all such boards, no matter what their surface, unsafe for fine artwork.
The common sizes of illustration board are 15" X 20'', 20" X 30", and 30" X 40". Boards of 40" X60" are manufactured but are difficult to find. Single-weight illustration boards range from 50 pt. to 60 pt. Many of the different surfaces are found in double weight and a few in triple weight.
RAG ILLUSTRATION BOARDS
Rag, or cotton, illustration boards are on the borderline between nonarchival and archival. They do not fit the definition of archival because they are often highly sized with alum and are therefore acidic. A board that is 100 percent cotton, like the Strathmore 500 series illustration board, which is the industry standard, is not greatly affected by a slightly acidic pH, nor, for that matter, are most of the artists' materials that would be used on it. In any case, this board is designed for use in producing fine artwork as well as graphic artwork and not for storing documents in archives or in protecting art in museum-style picture framing.
The 100 percent cotton illustration boards manufactured by Strathmore have a very durable surface and resemble bristol paper in their finish and working qualities when using various drawing materials and waterborne paints. Their greatest asset is their ability to stay flat under almost all conditions.
Cotton illustration boards are available in two weights-heavyweight, approx imately 65 pt., and lightweight, approximately 33 pt. The lightweight with reg ular (cold press finish) surface comes only in 22" X30". The heavyweight in regular surface and high (hot-press finish) surface is available in 20" X 30" and 30" X40".
An ARCHIVE is a place to keep records. Archival refers to something used in storing and preserving such as archival boards, which are used for storing and keeping artwork and records. The qualities that make a board safe for storing artwork and valuable documents have been evolving since the mid 1970s. The most desirable board is one that does not age, remains at a pH of 7, is totally inert, is iron- and copper-free, is inedible to insects, remains free of mold and mildew, does not condense moisture, yet is absorbent. The development of such a board is unlikely for many years. A more reasonable expectation for an archi val board would be that it is composed of either 100 percent purified cellulose from wood or 100 percent rag (or cotton) fiber and that it is at least 50 pt. thick. It should also be free of iron and be buffered to remain free of acid for seventy five to one hundred years under normal framing and storage conditions.
The logic for this is that a board made from cotton, rag, or purified wood cellulose is relatively inert, does not readily condense moisture, and is practical in that it can easily be cut to size. The thickness is important because it provides both a mechanical and a chemical barrier. Thicknesses of less than 50 pt. may not be sufficient to keep a moderate-size piece of art (26" x 36" or larger) away from the glass facing when it is framed. This is important because there is a natural tendency for artwork that is hinged to a mat, rather than glued to a backing, to curve toward the glass (see ).
Boards of less than 50 pt. are more easily subject, with changes in humidity and temperature, to developing buckles that can be transferred to the artwork that is being stored or framed. The same thickness is also needed to provide a chemical barrier from the acids present in polluted air and from such other storage materials as the backings used in framing or the wooden file drawers used for storage. Buffering of the board is mandatory, with the exception of boards made for the storage of albumin, dye transfer, and Cibachrome prints so that any acids from the storage environment and air pollution can be neutralized. Care must be taken by the manufacturer to be certain that there is no residual iron in the board that may accumulate in the washing of the fibers during processing. Any board that can meet these requirements and show no detectable deterioration for seventy-five to one hundred years should be considered safe and probably would remain safe for several more generations. The type of museum board currently in use has not been around for one hundred years, and all claims to permanency are based on theory and accelerated aging tests. In other words, everyone is attempting to make the best decisions possible with whatever information is currently available. It can be expected that new definitions and minimum requirements will continue to evolve.
"Museum board" is the common name for 100 percent rag or cotton-fiber boards that meet the current minimum standards for archival use. Museums were among the first major users of this type of board for storing and framing artwork, hence the name. At one time, this board was also called rag board. Because there are several types of boards that contain rag or cotton that do not meet the minimum standards for archival use, the name has slowly been replaced. Despite the introduction of conservation boards composed of purified wood cellulose, museum boards are still overwhelmingly the board of choice for archival purposes, because rag or cotton fibers are longer than those of purified wood cellulose and are, therefore, stronger and more durable. Any picture framer knows that it is much harder to cut a mat from a museum board than a conservation board, and that cutting blades wear twice as fast when cutting a museum board.
Several manufacturers produce a limited selection of colored museum boards. The Strathmore Paper Company, for example, manufactures two grays, five col ors, black, white, natural, and cream, all tested for bleed resistance, scuffing, rubbing, and abrasion to meet standards established by the United States Library of Congress. The thickness of its four-ply boards was originally between 50 and 55 pt.; however, Strathmore has increased it to 60 pt. to compete with the thicker boards now on the market. Museum board of a one-ply thickness between 12.5 and 15 pt. and usually available only in white-is used primarily for temporary storage and as a separation sheet when stacking artwork. It is also occasionally used as a drawing paper.
Museum board that is two-ply can often be found in the same range of size and color as that of four-ply, and is used for temporary storage for up to twenty-five years. It is too thin to be used in picture framing as either a mat or a backing. Both one-ply and two-ply are available in only 32" X40".
Museum board that is four-ply is most commonly used for long-term storage and museum-style framing. It is available in various shades of white and gray, as well as a limited range of colors, in 32" X40", and is also made in 40" X60". A new, still larger size, 48" X84", has begun to be distributed in some major cities. New and not readily available, six-ply and eight-ply are, in most cases, chosen more for aesthetic reasons in picture framing than for additional protection.
RAG MAT BOARD
Rag Mat is a 100 percent rag board with a buffered, fade-resistant, colored, sulfite-pulp paper facing. It is produced by the Crescent Cardboard Company. It is currently manufactured in twenty-eight colors, and new colors are soon to be introduced. The boards are available only in 32" x 40''.
The early versions of this board had a thickness of approximately 45pt., which was considered by many people to be too thin to keep most medium-size paper artwork away from the glass in picture framing. These boards are, how ever, being replaced with ones that are 50 pt. Rag Mat "100" is similar to the Strathmore museum boards, which are now produced in a thickness of 60 pt. in four-ply.
These boards are made neither from rags nor from cotton, but are composed of purified cellulose pulp from wood where the lignin has been removed and to which an alkaline buffer has been added. Conservation boards are made to meet the same requirements as those for museum boards, and are accepted by most institutions for use in archives. Some conservative conservators still question this type of board for long-term use because of the extensive chemical processing that the fibers undergo. They believe that the fibers are significantly weakened, affecting durability and possibly even permanency. Nonetheless, as rag and cot ton fibers become increasingly rare and expensive, conservation will become more common.
A large percentage of conservation boards available at this time are produced by three companies-the Rising Paper Company produces Conservamat, Andrews Nelson & Whitehead offers pHase 7, and the Process Materials Corporation offers Archivart Conservation Board. With the exception of the white and cream produced by the Process Materials Corporation, these boards are all between 50 and 60 pt. in thickness and 32" X40" in dimensions. Larger and thicker sizes are not generally available.
The color selection of conservation boards is much the same as the limited selection of museum boards, although black is not available. At one time, the gray pHase 7 boards used for framing changed significantly after a year or two, becoming lighter and developing a red tint. Today, primarily due to intense com petition, most manufacturers apply stringent tests to avoid such problems as fad ing. These tests, however, are accelerated aging tests, which only simulate certain aspects of the aging process and therefore cannot be a substitute for actual conditions.
The leading conservation mat board, Alphamat, made by the Bainbridge Com pany, is the conservation board equivalent to Crescent Cardboard's Rag Mat. Alphamat is available with paper-facings in sixty colors, which are pigmented to prevent fading. The board itself is a bright white. The bright white bevel, although eye-catching on white and off-white mats, is found by many people to be distracting on the darker and more strongly colored shades of mats. This board is designed for use in picture framing where the artwork is not touching the paper facing. Although several pastelists have used this board surface to draw on, it is not clear whether it is generally safe for fine artwork. The surface is a very thin paper adhered to an archival board and this combination would appear to be less hazardous than using a colored wood-pulp paper alone because, over the years, as the paper facing loses its strength, it has the board for sup port. In addition to the sixty colors available in 32" X40", nine are produced in 40" x 60'', but are not readily available. The boards are 55 pt. thick.
ARCHIVAL NONBUFFERED BOARDS
Albumen photographs, which were made through an early method of producing black-and-white prints with animal protein, and dye transfer prints, produced by a more modem and lightfast method of producing color prints, are both adversely affected by an alkaline pH, or a pH of more than 7.5. Dyed natural fibers, like silk and wool, are also sensitive to alkalinity because the dyes used in their production are usually acid dyes. It is therefore best to avoid buffered museum and conservation boards when framing albumen photographs, dye transfer prints, and work made of natural fibers.
Nonbuffered archival boards are very specialized, and are not readily available. The Light Impressions Corporation, however-a mail order house that sells a large variety of archival supplies to the public as well as to the trade-offers a 50 pt., four-ply, 100 percent rag board that is not buffered, in sizes from 811 x 10" to 32" X40". The company's address is: 439 Monroe Avenue, Rochester, New York 14607.
ARCHIVAL CORRUGATED CARDBOARD
The Process Materials Corporation produces a buffered corrugated board that appears identical to ordinary corrugated board, except that it is blue-gray or bright white rather than brown. It is called Archivart Multi-Use Board, and is available in both single weight (single wall), 1/8-inch, and double weight (double wall), ¼-inch in sizes of 32" X48", 40" X60", and 48" X96".
Archival corrugated cardboard is used as a backing board in museum-style framing and storage, as well as an artists' material. Although the purity of the wood pulp used to make this board is questionable, as is the quality of the adhesive used to hold the various layers together, the manufacturer claims it meets archival requirements. For additional security when using the board as an art material, I have had good results in creating rigid, and safe, painting surfaces by mounting 100 percent rag to this board.
FOAM, or FOAM-CENTERED BOARDS
FOAM BOARDS were originally developed for use in the graphic arts, but have now found their way into the world of fine art. Foam-center boards are light weight boards made of a rigid plastic foam with a paper or plastic facing. They resist warping, are more dimensionally stable than boards made from wood pulp, and are far less acidic. Despite the many advantages of this type of board over most paper boards, it cannot be considered archival because the core is poly styrene, or some variant of polystyrene, and this material naturally decomposes over a long period of time and is said to give off acid vapors. This aging process is greatly accelerated when exposed to ultraviolet light (some of the newer boards have UV stabilizers) and air pollution. Some manufacturers have begun to buffer the surface paper to help maintain an acid-free surface. In museum style picture framing, where foam board is used as a backing material, it is not exposed to ultraviolet light and the elements. This would make its use in framing quite safe as long as it is not in direct contact with the artwork. Unfortunately, some artists think this material is safe to use as a painting or sculpture material for fine artwork when they learn it is used in museum-style framing. Unless foam board is thoroughly covered-particularly the exposed foam edges-with enough paint to seal the surface from air and to prevent ultraviolet light expo sure, it will deteriorate too rapidly for fine art.
Foamcore boards are made with a polystyrene core and either a white clay coated or brown Kraft paper facing. The original white foamcore board was produced for the graphic arts industry by Monsanto and was named Fome-Cor. Today there are several other competitors, as well as a generic version. The way the polystyrene bubbles are formed during manufacture allows the edges to stay sealed, or at least crimped, during die cutting. This creates a characteristic pil low effect. It also means that any accidental impressions or dents can perma nently damage the board. The foam center is not affected by moisture, but the surface paper is, and outdoor use as well as wet mounting can be a problem. The surface will readily accept oil paints and acrylic paints, but the foam is sensitive to some solvents, particularly those in lacquers and shellacs. Fome-Cor cuts easily with a razor blade, if the blade is sharp and without defects; if it is not, it can tear the foam instead of cutting it. My experience with this particular board is that it behaves as if it had a grain and tends to cut well in only one direction. This board is commonly used in dry mounting and vacuum mounting, as well as in wet mounting when counter mounting is done).
There are three types of Fome-Cor: Original, acid-free, and super thick. The original is made in two thicknesses, % and 3/i6 inch, and four sizes, 20" X40", 32" X40", 40" X60", and 48" X96", of which the first two are most common. In the 3 1i6 -inch thickness, there is a greater variety of available sizes, but only the first three are readily found. The surface pH is slightly acidic, 5.5 to 6.5, and it is for this reason Monsanto produces an acid-free Fome-Cor where the surface paper is buffered to a pH of 7.5 to 8.5. The printed literature for this board suggests that it is archival and may be used as a substitute for museum board. This seems questionable because, for example, the surface of this board is made from a Kraft paper and not a purified cellulose, or cotton fiber. It is uncertain how much alkaline reserve the buffer can provide in neutralizing air pollutants and the natural formation of acid during the aging of Kraft paper. There are also questions about the permanency of polystyrene itself. This board is obviously an improvement on the original; nevertheless I have reservations about its archival qualities. The acid-free foam core is produced in thicknesses of % and 3/i6-i nch, and sizes of 32" X40" and 40" X60". The super thick variety, called Fome-Cor ST, is identical to the original board but is ¾-thick instead of 3/16 -inch. The available sizes are 30" X40", 32" X40", and 40" x 60".
Prime-Foam-X is produced by Primex Plastics Corporation. With all its similarities to Fome-Cor, it has some significant differences. The outer paper facing is thicker, whiter, and glossier. The formation of the foam bubbles and their higher density in this board allow for better retention of shape and minimize damage. This board is said to have "memory" because slight indentations tend to heal themselves. Consequently, in die-cutting the edges do not crimp or seal as they do with Fome-Cor. I have found that Prime-Foam-X does not have any directional cutting resistance and cuts well in all directions. It is manufactured in the same sizes as Fome-Cor and is also available in an acid-free version. This board is now produced with a UV inhibitor to reduce the possibility of ultra violet light breaking down the foam. There are two thicknesses-0.125 inch, or 1/s inch, and 0.210 inch, which is almost ¼-inch thick and is thus often referred to as ¼-inch nominal. Primex prefers to use thousandths of an inch rather than fractions in referring to thickness. The surface pH is between 6.5 and 7.0 for the regular surface and 7.5 for the acid-free surface. Prime-Foam-X is a little more expensive than Fome-Cor.
Gatorfoam has a foam center of Dow styrofoam polystyrene with a Luxcell veneer. The veneer is a multilayered, resin-impregnated, Kraft paper surface. Styrofoam is a much harder form of polystyrene foam and is much more dur able, but does not have any better aging properties. The hardness of the core combined with the Luxcell veneer results in a board that can only be cut with a table saw, which significantly reduces its ease for use in picture framing and storage. The major advantage of Gatorfoam is its thickness, which ranges from 3/16", to 1/2 inches. The 3/16", 1/2 and ¾-inch thicknesses are made in 30"x40" and 40" x 60". One inch and I½ inches are available in 48" x 96" as well.
Gatorfoam is manufactured with two surfaces, one white, the other brown.
The brown Kraft is better for receiving paint and for mounting. There are also two grades: Gatorfoam I is the standard, Gatorfoam II is a less expensive version with an expanded polystyrene foam center. This board is primarily used in model building and as a lightweight substitute for plywood.
Gilman board is like Gatorfoam II in that it has an expanded polystyrene core, which is also known as block foam. The outer sheeting, however, is a clay coated, white sulfate paper. This paper allows the board to be hand cut by first scoring with a mat knife and then bending, which makes it more practical for picture framing. Gilman board is produced in thicknesses like Gatorfoam-from 3/1 6 to 1 inch but only in 4'x8' sheets.
Artcore, manufactured by the Amoco Company, is not a paper, or a paper sur face foam board. It is entirely plastic. It is polystyrene foam covered with a white styrene sheet. Since it is all plastic, it is also waterproof. The surface sheet is treated with a UV inhibitor to reduce deterioration from sunlight and fluorescent light. The non-absorbency of the styrene facing can, however, make mounting difficult. I have had areas of several photographs separate from the surface after vacuum mounting. In fact, after experimenting with this board I have found it has no advantages for framing and storage over the paper-faced foam board. It would seem more practical for making displays, models, and signs. Its surface pH is 6.0 to 6.5, and it is manufactured in thicknesses of 1/16", 1/8", and 3 /16 inch. The available sizes are comparable to other foam boards.