Chemistry in the Workshop
I am not a chemist and CHEM101 was a long time ago. Some of the things described here are hazardous, but few are actually dangerous unless you're stupid or careless. And all of that is on you. I'm explaining what I do or have done and I've neither poisoned myself or burned my house down. Yet. YMMV.
Chemistry is a lot of fun as the second most practical science (after physics), there is a lot of interesting things you can do with common things around the house.
For instance, wood ash. You could throw it away, most people do. But it's mostly potassium carbonate and if you mix it with water, you get sodium hydroxide (lye). And lye is useful for all kinds of things from making soap to drain cleaners. If you want to try this, you should know this is one of those potentially dangerous things I mentioned. You see potassium carbonate is extremely hydrophilic and it will happily draw that water from your skin. And, as a bonus, as the lye forms, it will start to make soap from the oils in your skin. Cool, add more water and lather up! Actually that's going to hurt. A lot. Wear gloves.
As fun as stuff like that can be, we're here to talk about making and using period finishes. In this case, period is pre-20th Century. During this time finishes were one of four basic types:
- oil/wax
- paint
- varnish
- shellac
Modern chemistry added polyurethane and catalyzed lacquer. Both are fast drying and much harder than previous finishes. But they lack the warm and tactile feedback of earlier finished and I rarely use them even in my modern project (exception: table-tops).
Here we're looking at a brief overview of each finish, why and how it works and how to prepare it and use it in the workshop. Research on evidence for use can be found elsewhere.
Oil/wax
Using oils and waxes to protect or enhance the look and feel of wooden items has been going on since before recorded history. Linseed oil was used by the Egyptians who had a pretty good grasp of woodworking. Linseed oil is made from flax seeds (flax is grown for its fiber to produce linen). It's going to be common basically everywhere before, during and after the Middle Ages. And cheap. So, we'll take it as a given that it's an appropriate finish for furniture.
Another very common finish both on its own and in conjunction with linseed oil is beeswax. Rubbed into the surface of wood you get a nice finish, though not very durable. Applied over an oil finish, it looks even better and is the way we see it used later in period and into modern times.
Varnish
Cennino Cennini mentions varnish in his Il Libro dell'Arte and Theophilus Presbyter gives two recipes for making it in his early 12th Century De diversis artibus. His varnish recipes are basically the same as we have from post-Rennasiance authors like Andre Roubo (L'Art du Menuisier, 1769).
