[Virgil Elliott]

There are other mediums out there called amber mediums, which may or may not actually contain any amber resin, so unless I were to know which amber medium you're talking about, I can only make general comments. These all contain resin or balsam (coniferous tree sap), cooked oil and solvent. With Blockx, the oil is poppy oil and the solvent is spike oil, aka oil of aspic. There is another one by a small manufacturer that has a balsam and cooked oil in it, either walnut or linseed, a solvent (probably turpentine) and maybe some amber or copal resin in it, and there might be a few others out there with who-knows-what in them. The only one of these manufacturers whose word I would trust on what is in a product is Blockx.

Whether lots of people like to use a given medium or not is no indication whatsoever of its archival properties, nor is the apparent condition of the paintings in question when they are less than 100 years old. The people whose opinions I place greater credence in regarding these matters are the top museum conservators, who see and restore old oil paintings on a regular basis and are plugged into the international conservation community's information network. In that field, it is widely acknowledged that resins and balsams in old oil paintings are generally problematic, and that the oil paintings that have weathered the centuries best have no detectable resins in the paint layers.

Resins lack flexibility, and that is obviously a factor in the cracking of old paintings. One might or might not get by with a very minor addition of a resinous medium to one's paints, depending on many other factors. With a rigid panel support, the problems of cracking would be greatly reduced over paintings on stretched canvas.

Resins discolor, i.e., turn yellow and, eventually, brown. Bill Whitaker discovered this with his damar varnish. Once a resin has turned dark, it stays dark. It cannot be bleached back to its former appearance the way a yellowed linseed oil paint film can, by exposure to light.

Cooked oils are also looked upon as troublesome compared with unheated oils, as they are pre-oxidized (stand oil being the exception because it is cooked in an oxygen-free container).

Solvents also adversely affect the strength of oil paint films.

The mediums in question are composed of resin (and/or balsam), cooked oil, and solvent. There may or may not be driers added by the manufacturer, usually cooked into the oil, and that is another potentially problematic ingredient in the mixture, according to the best information I have come across in my studies on the subject and from my consultations with conservation experts at the National Gallery in Washington.

The 17th century artists who employed cooked oil mediums and/or cooked oil with balsam or resins only used these mediums for certain special effects in the final stages of the paintings, with most of the work done with paints composed of pigment and linseed oil, uncooked and with no resins or balsams in them. Walnut oil was sometimes used instead, but mostly it is linseed oil. It was not a matter of adding medium to all the paints, the way people love to do today. These paints were mulled to the desired painting consistency from dry pigments and unheated linseed oil, so there was no need to add anything to them. The Old Masters were not painting with modern tube colors.

In the mid-18th century is when painters began using exotic concoctions more extensively in their paints, and it is these paintings that have suffered more severe consequences as they have aged. Sir Joshua Reynolds is the poster boy for bad choices of materials, and it is probably his influence that made these concoctions popular in the first place. Reynolds's paintings are notorious in conservation circles for the many defects they have developed and for being among the most difficult to restore. Whereas the paintings of Rembrandt, a century or more older than Reynolds', have held up much better over the ages, with no resins in them. I think that is significant, and worth serious consideration.

Each painter can decide for himself/herself how important it is that the paintings he or she creates continue to look the way they look when they paint them, and how far into the future this matters. If one cares, it is probably better to leave the resins out of the paint. If one doesn't care about the future, it doesn't matter what one uses.

Virgil Elliott