Tinting Strength

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)

The single best way for a non-scientist to determine the value of their oil paints is by performing a tint test.  A tint test reveals the ability of an oil color to maintain its strength when mixed with white.  This test for pigment concentration provides a method of comparison between brands of paint if the pigment used by each is exactly the same.  Frequently, the name of the color on the tube does not necessarily indi­cate what is in the tube.  For example, in the manufacture of the common color Raw Sienna one manufacture it from the traditional pigment found in Siena, Italy, or one could manufacture it from the chemical, iron oxide.  The one made from iron oxide will have a stronger tinting strength and appear to have more pigment.  Something treasured with expensive colors like those made from cadmium and cobalt.  With Raw Sienna, a relatively inexpensive color, the issue is not the tinting strength as much as it is the pigment itself.  The natural pigment mined in Sienna is not pure iron oxide but a mixture of iron oxide and silica.  The silica makes the color more transparent and imparts a weaker tinting strength since there is proportionately less iron oxide.  It is exactly these characteristics that make this natural weaker pigment more desirable for painting landscapes and portraits.  Therefore a fair test can only take place when the pigments are precisely the same.  This is why information such as C.I. numbers and names would be so helpful in comparing paints.

Within two brands of paint of equal grade, about 25 to 50 percent will cross match using the same single pigment for a particular color. It is important to avoid testing colors that contain several pigments, even if they are identical, because they are likely to be in different ratios.  It also only makes sense to test the most expensive colors for two reasons.  First, if a manufacturer is going to short a color they are going to do it where it will save them the most money.  Second, testing the expensive colors could end up providing you information that could save you dollars and testing the inexpensive colors would save you pennies.  Since a tint test is to discover if you are getting the best value, it is vital to note the volume of the tube of paint.  The so-called standard size tube is not so standard.  The “standard” size can be a small as 34ml and as big as 40ml, as much as a 15% difference.  It is not uncommon to find the 34ml tube selling for less than the 40ml competitor’s tube only to realize that the “less expensive” 34ml tube cost more per ml than the competitor’s 40ml tube.

Once two identical pigments from two different brands have been identified,  you can perform a test mixing half zinc white with half color, and then take half of that mixture and mix it with half zinc white again, and repeat this procedure several times for each brand until you end up with white.  This will give you a serial dilution, which can then be compared and the one that requires the most dilutions has the most pigment.

Very small differences between brands in tinting strength are best ignored because the most concentrated use of a pigment to make a color is not always desirable.  At some point in the valuation process the consistency of the paint or the specific hue of a pigment becomes a more important issue than subtle difference in concentration.  Paints made with too high a concentration of metal pigments such as cadmium or lead become so thick and cakey that they cannot be easily expelled from the tube or manipulated on the palette.  Paints made with some of the newer synthetic pig­ments, such as phthalocyanine, have such high tinting strength that if they were used in high concentrations, they would totally overpower any color mixed with them.  Because of these factors, manufacturers balance the level of concentration with the working consistency.  Any home‑done tint test comparison needs to be judged against your aesthetic preferences for the particular paint.

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)