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16003RE: [MedievalSawdust] Milk paint

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  • Vels inn Viggladi
    Sep 11, 2013

      >So is milk paint period?  Can anyone
      document a period milk paint recipe or artifact that uses it?

      Presumptively, yes. But it's tricky to prove definitively.

      I beg you'alls indulgence on this, milk paint is one of my rant inducing topics -

      Cennini dedicated a fair part of Il Libro del Arte to discussing different adhesives. Almost off-handedly he mentions the use of these sizes as binders for pigment. Paint is composed of three elements: pigment, binder or temper, and solvent. You have the color, the carrier for the color, and the solution that things the carrier so it can be applied to a surface.
      Binder and temper are words that can be used interchangeably. Two other words that are also used in the same context, interchangeably, are size and gluten. Size and gluten more typically refer to a binder that is an adhesive rather than one that is primarily a temper. Of which, Cennini discusses seven total recipies for "size." Five are made from animal skin or parts, one from thin cheese, and one from crushed amber. The wrench in all this is his discussion of varnish as a "gluten" made from crushed amber boiled in linseed oil as a hardening finish. Gluten is apparently the closest word in English that relates, and is actually a declension of the latin word for "glue." In looking at the original Italian, Cennini only gets specific when speaking about oil (binder and solvent) paints for painting canvas. Far more often he will interchange "temper" and "size" when discussing other paints.

      For a casein paint, the pigment is whatever kind of dirt one is using for color, milk proteins for a binder, and water for a solvent.

      Many consider Stephen Shepherd to be the head man in the field when discussing pre-modern glues and paints. His literature indicates that the method for deriving casein powder from milk does not predate the US Patent for doing such, which was submitted in 1847. While he once stated that milk paint was never used on furniture in the 19th century, he also claims that milk paint is a white-wash, and not a paint. Pigmented or not, he holds it is a white-wash... He moved the goal line to stay right. He eventually agreed that he didn't have significant information about the topic prior to the 18th century and allowed that there are other methods of attaining casein protein than the modern method which was patented in the 1840's. This limited his one-time certain statement that "milk paint was never used on furniture" to be revised to "milk paint does not appear to have been used on furniture in the 19th century."

      Rarely are the paints we find on extant furniture pieces tested for chemical make-up. Often, many of the extant pieces from the middle ages have been stripped of their original finish (paint) by Victorian era "conservators" who were attempting to protect the wood under the failing original finish by removing old finishes and replacing with oil and wax (in accordance with the style choices indicative of their era). There are a few pieces that do still have traces of their original paint, and have had the paint tested for chemical makeup. The "Duchess Agnes" chair is one of them and is typically my go to. The paint is identified as "proteinaceous." That is, the binder is some form of animal-derived protein. Forensic science has not been applied more thoroughly than that, however. We do know that 17th century pieces from New England have also been tested and confirmed to have protein-bound pigments. Those are believed to be hide-glue sizes. The double check, however, is that not all the pieces found with  proteinaceous paint have hygroscopic properties -- that is, they don't absorb water and become fluid again when wet and/or warmed.

      No one can say with certainty from the chemical tests, usually because the molecules are so deteriorated they cannot be identified beyond being a protein strand, and we have no written documents that provide a certain answer from within our period of study.  Collagen tempers (Hide, Hoof, Isenglass) are hygroscopic. Casein (Milk/Cheese) tempers are not. Egg temper is also non-hygroscopic. But that's where we get into how the paint adheres to the wood. Egg tempers have a tendency to float on the surface of wood, while Casein is a penetrative temper. So, now we're looking at how the paint has worn off...
      The Duchess Agnes appears to have had a penetrating temper, that is not hygroscopic, and is proteinaceous. It's a process of elimination argument.


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