|Woodworking can be a science project|
On the other hand, there are a multitude of areas in life — especially in the arts and crafts — where activities and functions, and success or failure, are determined in great part by the understanding of science, even if you don’t think about it explicitly.
I remember once engaging a self righteous “academic” who believed that wood finishers were essentially glorified ditch diggers, that we employed no real science or technology in our work. After presenting him with the following, the conversation suddenly ceased to be a conversation. I was on my own with a soliloquy at that point.
So, if you ever get the temptation to either think that because you are a finisher you are some sort of Cro-Magnon, or have an insufferable in-law who is embarrassed by what you do and possesses the dim-wittedness implied by it, toss this little piece their way.
The practice of furniture finishing and restoration requires the practical application of many technical and scientific disciplines. To competently complete his task, the artisan must be learned in physics, chemistry, materials science, biology and physiology in each project. For the most part, practitioners are too busy getting the job done to truly reflect on the technological sophistication of their projects, so I’d like to point out some of these truths.
The applications of chemistry to finishing are nearly endless.
Organic chemistry leads us to polymer chemistry, which in turn is generally dependent on the nature of the physical chemistry and thermodynamics and reaction rates. (I think I hear eyeballs rolling back in their heads right about now.) The chemistry of resins is all about polymer chemistry. How hard or soft is the finish? How tough or brittle? How transparent? The saturation of the surface is almost entirely dependant on the molecular weight of the resin, which is why a hand-rubbed shellac finish (very low molecular weight) looks absolutely delectable, while a sprayed epoxy or polyester finish (very high molecular weight) has a very “plastic” appearance.
Even the delivery method and formation of the finish film are dependent on the chemistry of the materials. The more you understand this, the greater your predictive success at the workbench when you need to tweak the process. Solvent interaction and effects on coatings performance is one of my own great interests, as it expands my options immeasurably when it comes to manipulating and using coatings systems on a near-daily basis. How well something is dissolved by something else, and how rapidly it occurs or is reversed, is a purely chemical question for the most part.
Much depends on optics and visual perception (see physiology below). In order for the human eye to perceive color — and perceive it correctly — there must first be a light source. The nature and color spectrum of that light source makes all the difference to the finisher “getting it right.” In principle, you can get close results in almost any lighting system, but for the best results you should do all your finishing work with lighting that mimics that of the furniture’s final location. Otherwise you might be a victim of phenomena known as “color constancy” or “metamerism.” An example of this is when you do final color matching late at night under cheap fluorescent lights, but by the light of morning you didn’t get close.
In fact, every aspect of appearance can be traced to the physics of the materials. As I mentioned before, the molecular weight of a polymer affects the nature of the light absorbed, transmitted, or refracted (bent) by that material. In addition, the ability of a coating to reflect light determines the gloss. If light is left organized in its reflection, we define that as high gloss. If the light is scattered by either the topography of the surface or by light-scattering particles just below the surface, we get matte finishes.
Working at the right temperature is critical to virtually every aspect of film formation and manipulation. Applying a solvent release coating (cellulose nitrate, shellac, etc.) and leaving it in the sun can result in disaster as solvent bubbles form in the curing film. Who knew that the classical gas laws we learned in ninth-grade chemistry (especially Boyle’s Law) had a critical role to play for our work?
Materials science is an amalgam discipline that concerns itself with the physical nature of materials: their creation, properties, and manipulation. In essence, it is the melting together of all the concepts of chemistry and physics together into one untidy whole. If I had to do it all over again, I would have probably majored in materials science in college, rather than chemistry, art and art history. Materials science is just plain fun to me.
Here are some of the considerations blended into the world of materials science:
Synthesis includes formulation, physical chemistry, configuration, and a thousand other considerations when designing and creating a coating material and all the portions of the system in which it might be used.
Rheology is, strictly speaking, the study of material flow, but, practically, it is defined in terms integral to the function and performance of finishing materials — hardness, flexibility, brittleness and toughness. This goes not just for film-forming materials, but also adhesives, fillers and any other part of the composite structure.
Appearance is such a complicated phenomenon with materials science that it overlaps with every other science discipline in this list. Why? Because the elements of appearance include: lighting color and source; the “observer”; color (which is itself a compilation of discreet components called hue, chroma, and shade); transparency; texture; gloss; and “colorant molecular architecture”, e.g. natural plant dyes vs. synthetic directional pigments. You have just described the elements of achieving any particular finish, especially the matching of an existing one.
The world of biology is a far-flung one, but there is a lot of it in wood finishing in the guise of deterioration, physiology, and agriculture.
A lot of deterioration is biological in nature and driven by the environmental processes necessary for life. Rot? Mold is really fungal activity, so count in mycology. Ditto mildew and related staining. Insect infestation? Make a check mark for entomology. Rodent damage? Mammalogy.
Visual perception is a fundamental physiological phenomenon. The individual components are so numerous it is nearly impossible to create a concise snapshot. In just the eye itself, there are issues of color acuity or color blindness, lens transparency or coloration, retinal condition, and how good is your cornea. Check ophthalmology.
How about the hand skills required to manipulate materials skillfully? Enter kinesiology, the study of human motion.
And what about the “natural” resins we use widely, things like shellac, damar, copal, colophony, etc. They are all agricultural products, with all the vagaries that implies. Some are from the insect world (shellac) most are from the realm of tree exudates.
And then we move on to the effects of all the chemicals we use on our bodies. All chemicals are problematic under the right (or wrong) conditions; any chemical can and will kill us. If we are using poisons, we’d better be functionally well-versed in toxicology (the dose makes the poison). Many of the tree-based resins are polyterpenoids, which are among the most virulent allergens known. Hello, you’ve just been introduced to immunology.
Anyone who does what we do skillfully is a scientific scholar of the highest repute, even if they don’t know it.
Don Williams has been a furniture finisher for more than 35 years. He is Senior Furniture Conservator at the Smithsonian Museum Conservation Institute.