There seem to be increasingly varied selection of painting mediums on the market to give artists better all round handling properties to their paint. Most of these mediums are based on older 19th c recipes that were tested and found inadequate for permanent oil painting use. But painting manufactures are now producing “improved” versions of these, some with varying degrees of Alkyd Resin to improve the product!
I want to discuss these mediums in order of what seems the most relevant to the average painter, so I’ll start with Alkyd Resin, its introduction and various uses:
The first real Alkyd resin medium was produced by W&N in the 60’s (Liquin), this was produced as an all round painting medium for use with oil paint and had a primary benefit of its fast drying properties.
It is hard to find information on the exact ingredients in Liquin, but the following gives at least a summary of the contents (this info was produced as a data safety sheet – note the actual percentages of ingredients are missing):
2-butanone oxime Xn;R21. Carc 3;R40. Xi;R41. R43.
96-29-7 < 1%
Cobalt Carboxylate ( 18% Co ) Xn;R22,R65. Xi;R38. R43. (used as oxidative polymerization catalysts, in general terms a drying agent)
distillates (petroleum), hydrotreated light Xn;R65. R66. (some form of mineral spirit solvent)
Oil modified alkyd resin R66.
30-60% (this is the alkyd bit, note that the oil additive is not identified)
Cobalt driers are added to cause drying and can be added to any oil medium to increase the drying time. Particular negative qualities of metal dryers are that they dry the painting layer too quickly and can cause cracking of the paint layer over time.
A mineral spirit is used to liquefy the medium, again I’m not exactly sure what they are using here.
Alkyd resin has to be mixed with some form of oil to stimulate drying (some ‘short’ Alkyd mixes, or Alkyd with low levels of added oil have to be oven baked to dry) as W&N (to my present knowledge) does not disclose the ingredients we can assume that the oil might be included in this list of common alkyd oil additives:
Coconut Oil (commonly used)
Corn Oil Cottonseed Oil
Linseed Oil (commonly used)
Soybean Oil (commonly used)
Menhadden Oil (fish oil derivative)
Alkyd is a synthetic resin invented by General Electric in the 20’s to coat electrical wiring. Alkyd has to be mixed with an oil medium so that it actually dries, the benefits of alkyd are it’s quicker drying properties, but the manufactures admit that the oil drying mediums still yellow to some degree (in relation to the drying oil used).
(Rustolleum is an Alkyd based paint also good quality exterior varnish is often Alkyd based)
There is a great deal of publicity from paint manufactures and hence internet painting sites extolling the virtues of the various Alkyd mediums on the market. At the same time very little information on any negative attributes of Alkyd as an artists quality medium, and particularly very little information on the conservation properties of Alkyd resin. W&N Liquin is probably the oldest medium that might be tested, but I understand that the formula has been revised a number of times over its 40 plus year history so information on its aging properties will be unreliable.
To place Alkyd Resin in context compared to other resins in various mediums that can be used, I would firstly ask what properties single it out as being of particular benefit:
The single most attractive property of Alkyd is its relatively quick drying time, although I am a bit confused whether this is a property of Alkyd or the metal dryers that seem to be mixed with most alkyd mediums. I was always taught that the paint layer has to be given time to dry at its own pace to avoid cracking and adverse movement between paint layers. Metal, or in particular cobalt dryers can be added to any home made medium, or simply linseed oil to enhance drying time with the advantage that linseed oil is a tried and tested oil with no hidden ingredients.
The second real property of Alkyd resin is its durability, in fact alkyd resin is used in the better exterior floor varnishes for its stability and durability. Again, dependant on the quality and quantity of oil added to the resin (as with all resin/oil mixtures) the resin content gives a tough film but also imparts brittleness to the paint film. From my own experience the modern varnish mediums are excellent for 10-20 years, remaining flexible and durable, but do become brittle and either flake or crumble with exposure to light and moisture (the remaining corroded varnish layer proving difficult to remove for replacement purposes), a well looked after oil painting using an Alkyd medium might only exhibit these traits over perhaps 50/60 years.
A well made Damar and Linseed oil/stand oil medium will create a good durable paint film (and you can add a percentage of dryers if this is absolutely necessary), the paint layer may not be quite as tough and durable as Alkyd, but that quality of toughness really does trigger alarm bells in terms of the eventual brittle quality of the surface. The Damar medium also has the benefit of being a tested Resin that has apparently superior properties to many other resins that were considered sound in the 19th c (most notably Mastic Resin and the problems with Meglip mixtures). The only other notable comment about detrimental qualities of a Damar medium is a slight propensity to yellow over the years. But as already mentioned, Alkyd (at its best!) uses oil dryers and possibly linseed oil so will not differ in this respect from Damar medium. (I also am concerned about the many alternative oils that could be contained in Alkyd medium, most that would be seen as completely unsuitable for artist quality use.)
In conclusion, within my own work and my use of artists quality materials I am extremely conservative, only using materials that have been thoroughly tested by the passing of time (a hundred year period would be a minimum testing time). I try and keep things simple and not over complicate technique with the intrusion of differing mediums, oils and gels. I certainly would not use a product that contained ingredients that I did not know! Alkyd resin mediums may well be a wonder product that will last for a very long time (no one really knows!); but for my part I will stick with what is known, and not risk the alternative that could lead to extremely bad conservation issues with paintings 50/100 years down the line.
I admit that the current hype surrounding the range of new mediums on the market does worry me, the ‘publicity capability’ of the larger paint manufactures far exceed individual artists concerned miss-trust and input, so swamping information available on the web and giving a very one-sided picture of these products.
When I first studied painting 28 years ago Liquin was becoming ‘know’ as a product, and there was a very healthy miss-trust of its properties and durability. On the whole Artists would not use it, but commercial illustrators used the medium for its drying properties (I also worried that the medium seemed to impart a grayish sheen to the picture surface - not sure if it still does?). That 28 years period seems a very short time for Alkyd to have become fully accepted as a standard validated medium.