Final varnish

[Richard Bingham]

Jennifer, for an artist to test materials in the studio, one realizes first off that we don't presume to have a command of either organic chemistry, nor of laboratory grade procedures and equipment.

The first test is quite naturally, one of a simple "hands on" assessment. Does the material "do" what you want it to? Does it handle to your liking?

Tests for permanence are rather more subjective, as there may be a great number of variables which will be out of one's control as soon as a painting leaves your possession. I rely on a rather "dumb brute" method for testing my materials, simply subjecting test samples to outdoor weather. I place test samples of painting supports, paints, mediums, varnishes, etc. outdoors on the weather side of my studio, and leave 'em there. Between exposure to sunlight, temperature variations from -20F to over 100F, rain, snow, hail, sleet and frosts, a pretty good picture of a material's failure modes emerges. Naturally a painting would never be subject to that kind of abuse under normal conditions, but weather provides a semblance of accelerated aging. Naturally, it's not going to cover all the bases.

Learn as much as you can about materials from reading. To keep it very simple, my favorite book on that subject is Frederick Taubes' "Studio Secrets" alas, now out of print. Unlike a number of latter-day self-proclaimed experts on the subject, Taubes was a practising studio artist who based his methods on what is known of traditional "old master" technology, and as an entrepeneur who marketed painting materials and mediums was actively involved "hands on" in his business. He wrote the technical column in American Artist from 1942 until well into the 1950's, and taught materials and methods courses in seminars he gave around the country.

I think every artist who paints in oils should own a copy of Ralph Mayer's "The Artist's Handbook of Materials and Techniques". It contains a lot of sound, basic information, although it is overly ambitious in scope, and suffers from the fact that Mayer was more an "armchair" type who relied heavily on "hearsay" and recapitulating information from other sources as opposed to verifying the book's contents through his own working experience.

Beyond that, discussing materials and methods with your peers is almost always instructive (one way or another) but can be a minefield of errors and incomple information and bad practice. One should have a clear working knowledge of painting materials and procedures and a means for testing all the ideas which abound, rather than blindly following anyone's "prescriptions". It sounds forbiddingly complex, but hey, it's not rocket science, and the basics are very simple. All the complexities are either overlapping redundancies, or extrapolations which can fall back easily upon the knowledge of basic, sound painting practices for clarification.

Since I'm feeling reckless, (read stupid?) I think your questions about mediums would be better addressed in another thread, which I'll open in response to them. Claudemir wisely notes that the subject of painting mediums is one which is very personal with almost everyone who paints in oils, and has caused some dandy knock-down-drag-out flame wars on art fora as well as in person, when artists meet.

[David Clemons]

Originally Posted by Richard Bingham:
...Marcus, the principle is correct, but you have it reversed. As paint films continue to dry and give up their volatiles, they shrink They do NOT "grow"...

While I wouldn't refer to it as growing, from what I've read drying oils do expand, possibly as much as 15-25% as they absorb oxygen, and then will gradually lose volume as they release their volatile content over time. This can lead to cracking issues on a top layer surface which itself has already dried. The volatiles which may include acids and alkenes can also stay present in the paint film and react with some types of pigments, which may lead to discoloring with any top layers as well.

[Richard Bingham]

Originally Posted by David Clemons

. . . from what I've read drying oils do expand, possibly as much as 15-25% as they absorb oxygen . . .

Try this experiment. Put just enough linseed oil in a palette cup to cover the bottom of the cup, and "pull up" visibly on the sides (that would be about 1/16" "deep"). Leave it in a warm, well-ventilated place (plenty of oxygen). At what point do you note expansion of the volume of oil by as much as 10%? What is the nature of the surface of the dry oil film as soon as the puddle of oil "skins over" ? Is it bloated, like a little bubble because of the volume of oxygen being absorbed, or does it resemble a raisin, shrinking in the sun from the loss of its liquid components through evaporation?

When linseed oil is heated to approx 475F in a vacuum in making stand oil, there is a slight noticeable increase in volume, as the purpose is to partially polymerize the oil, which requires the addition of oxygen, but that's not a dry film state.

[Jennifer Bogartz]

Richard, I couldn't find Frederick Taubes' "Studio Secrets" at my library but they did have a couple other of his books, both on oil painting, and I put them on hold along with Ralph Mayer's book.

[Richard Bingham]

Jennifer, try Abe Books online for books out of print. I was able to "score" a couple of copies of "Studio Secrets" for my students very reasonably a few months ago!