Since my initial visit to Kremer Pigments, I have felt increasingly uncomfortable with the idea that, on the advice of two of their employees, I was going to put turpentine and amber in a pot and cook it on my kitchen stove. In my twenties I spent a few years working in art supply stores and, if I may be considered a representative cross-section, there is about a 90% chance that the advice I received at Kremer was wrong. So last night I spent a few hours reading and have had some of my concerns addressed. It turns out that the clerks I consulted at Kremer were misreading Kurt Wehlte's entry, Amber, a Hard Resin, in The Materials and Techniques of Painting:
Some amber is exceedingly hard, softening at approximately 250°C and melting between 290 and 300°C. This fossil resin cannot be dissolved directly, even in hot drying oils, but must be fused or "run" first.... Attempts to dissolve amber directly in turpentine succeeded on a small scale in the laboratory, thanks to some ingenious tricks, but these were without practical value.
The phrase that stuck out as most troubling (besides the extremely high temperatures and "without practical value") was "must be fused or 'run' first." There is no mention of melting in turpentine at heat or of the conditions required for fusing the amber. Additionally, I have no ingenious laboratory tricks up my sleeve. After a few internet searches I found a couple of helpful references on violin making and woodworking blogs. This entry posted in May 2007 by someone calling themselves Fridolin is particularly insightful:
I have recently started making my own amber varnish. I have found the descriptions given in Geary Baese's book on the old italian varnishes to work for me. The difficult part is to fuse the amber, which requires A LOT of heat. In my experience 300°C is not enough. I use special lab equipment (glassware and electric heat source). You also get a lot of toxic and smelly fumes (It can not be done inside). Once you have fused the amber, it easily dissolves in linseed oil (at a much lower temperature) and it gives a very thick varnish that dries within 24h in my UV cabinet.
In the 18th century, when amber varnish was more widely used, it must have been obvious that the amber needed to be fused before adding it to the oil. In fact, Fridolin's choice of words, "Once you have fused the amber, it easily dissolves in linseed oil," matches Hansard's Baskerville recipe exactly. Clearly, my little jam jar of linseed oil and amber will never transform into Baskerville's magic ink of its own accord. Quickly, I began searching for Mr. Geary Baese's magnum opus on old Italian varnishes. Google books has scanned one copy but does not have the rights to make it available. They list Baese as the publisher and that the copy they scanned is at the University of Michigan. Searches on bookfinder, abebooks, and Columbia University's online catalogue yielded no copies. Searching for information on Baese I found this foreboding entry from 1995 on the website of Alf Studios Concert Violins:
The pure resin varnishes he uses cost more than $10 an ounce from Geary L. Baese, 610 W. Mountain Ave., Fort Collins, CO 80521, but don't bother contacting Geary unless you are a committed violin maker.
Not only am I not a committed violin maker but.... Google searches yielded no further information on Baese. ¶My next search for amber fusing techniques brought William Theodore Brannt's, Varnishes, lacquers, printing inks, and sealing-waxes: their raw materials and their manufacture, (1893) to my attention. After reading this passage on page 45, I began to have some serious second thoughts:
In fusing it [amber] suffers decomposition. It gives off water, succinic acid, marsh gas, and a mixture of liquid hydrocarbons (known as oil of amber), while a more or less dark-colored substance, the so-called amber-colophony or fused amber, remains behind. This amber-colophony is the substance which is especially prepared for the manufacture of lacquers by roasting amber.... The oil of amber, which in fusing amber may be obtained as a by-product, forms in a refined state a pale-brown fluid of a strong, disagreeable odor. The crude oil is dark brown, and possesses a very repugnant odor.
After reading this enticing description, I began searching for where to buy already fused amber rather than searching for how to fuse amber. The first hit was a 10ml (2/3 tablespoon) vial available from Dick Blick for the discounted price of $133 and change. Successive searches found a number of small workshops making amber linseed varnish at a more reasonable price. I have decided to leave that stage of the process to other craftsmen.