During the rise of the University in Medieval and Renaissance Europe, a student earned his degree not by regurgitating the facts taught to him by his professors but by disproving the “facts” as taught. Rote education was the mainstay of skilled trade education (usually via the Guilds during that era). In an ironic twist, today I find that disproving my instructor is in relation to the “facts” he has presented regarding skilled trade.
I have been reading Stephen Shepherd’s “Full Chisel Blog”. When I began delving more deeply into historical furniture construction and technique, his book on Hide Glue became a highly valued tome. While most of the information presented in that volume is culled from sources well later than the typical eras I have interest, the information is well presented and of exceptional use. Reading more of his blog, I found him to be delightfully eccentric and showing a breadth of knowledge. He’s no one trick pony. When it comes to the peculiars of 19th Century American Frontier Woodworking, he is short on equals. Before the 19th century, well… let’s just say I threw a brown flag when I came across this post on “Milk” Paint.
In particular, I take exception in his claim that at no time prior to 1841 was Milk (Casein) used as a binder for pigment in paint. Mr. Shepherd does caveat that Cheese (Casein) was identified in historical sources prior to the 19th century. It rather clear that Mr. Shepherd has failed to learn the process for making Casein for paint. The process (described at least as early as the 14th Century) for making Milk Paint involves curdling milk and separating it to create the size. That is, taking whole milk and turning it into a quick cheese to begin the process. This is a different process than that patented in 1841 to make powdered skim milk, which is wrongly attributed by the good sir to be the origin of Milk Paint, though it provides similar result. Simply, the difference between “Milk Paint” and “Casein Paint” of any name is the marketing name.
Cennini describes the process for preparing five different sizes or tempers for paint, what we’d modernly refer to as a binder. This includes both fish and hide glue (of several varieties), druggists’ glue (gum arabic), cheese/milk, and egg yolk. He additionally provides details on the use of linseed, walnut, and olive oil as binders for specific artistic uses. Diverging, though van Eyck (a contemporary of Cennini of greater fame) is sometimes credited with the innovation of oil paints, Theophilius described their use well back in 1125. Still, the popularization of oil paint for artwork can be accurately applied to van Eyck in the early 15th Century. As an aside, this also predates Mr. Shepherd’s assertion of his oldest found reference to painted furniture in “modern” sources was in 1225. And while literary sources for painted furniture may not have been identified until even the time of On Diverse Arts, I’d have to wonder what he would make of the colored furniture indicated in Ikons and Illuminated artwork going back to the Second Century Encaustics.
Somewhere in this Mr. Shepherd has decided that whatever Casein Paint that did exist prior to and after 1841 is not paint at all, either, but “Whitewash.” To follow that bit of logical acrobatics is not too difficult, though still incorrect in summation. It is posited in his pair of articles that Caseins are whitewashes because of the inclusion of “whitening” when preparing the pigment. Whether this whitening be lead, chalk, or some other white-colored agent, they all fall under the same heading. Though these agents are white in color and may be used without other pigment in a temper to make a white paint, they are not “whitewashes” unless they are used without other pigment. This is one of those cases where the shifts of language can trip even the most educated historian. “Whitening” does not mean an agent that makes something “white,” it means an agent which makes a pigment opaque without requiring an overabundance of pigment for opacity. Given the conditions of the pigment and the size used, there are a significant proportion of paints which cannot ever achieve opacity. The second fault here may also come from inexperience. Milk is certainly white, as is curd and modernly processed dry casein. To presume that any size or temper or binder made from this chemical would also be white is simple. That presumption is, however, not correct. Before any pigment or whitening is added to prepared Casein (that is, mixed with water to create a size), the mixture is a yellow-brown. When it dries without having any pigment introduced, it becomes a slightly translucent yellow-brown. It’s actually this color that off-the-shelf “Yellow” Wood Glue mimics.
Mr. Shepherd’s love affair with hide glue does not seem to have led him to fully investigate the history of other glues, of which modern plastic white and yellow wood glue were derived to mimic casein glues. Elmer’s school glue still is a casein glue. I’d also say I was disappointed to find he only made passing and oblique reference to Cennini in his book “Hide Glue: Historical & Practical Applications” that does not even include an actual citation despite three recipes for hide, one of bone and one of fish glue being found in “Il Libro dell’ Arte.” But, that is all far afield this discussion of Milk Paint. Somewhere in between is to note that Cennini describes various sizes and tempers (or binders) for pigment to make paint, then goes on to interchangeably describe using a size or temper for making paint, without usually specifying which binder to use. In any case, 1125, 1437 and 1841 rather succinctly brackets the dates for this entire discussion.
Whitening is important in any paint, as said, for providing opacity. Regardless of the temper being oil, egg, or other, adding a whitening agent is necessary for many natural pigments. Lead white was used until the 1970’s as a whitening agent in commercial paint because it so wonderfully filled the need to make opaque paint without an overabundance of pigment. Choosing to ignore anything but oil to define as paint, or to decide through misunderstanding of language that to use opacifiers equates to making a whitewash, is at the very least objectionable. For such to come from someone who presents as an expert in such historical matters it is far more than objectionable, but neigh unforgivable.
I expect I will be writing more on historical paints in articles to come. The preparation and use of paints in portraiture and decoration are very diverse and broad. Though Milk (Casein) Paint has become my preferred “go-to” for those furnishings I do paint, I am looking forward to experimenting with several other binders and writing about them. I have particular reasons for choosing Casein Paints over some others, and we’ll get into that another time as well.
As much, I do aver that I have disproved my instructor in this matter and thereby prove my bona fides for matriculation in this subject.