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.

This article is a survey of period finishes. In this case, period is pre-20^th Century. During this time finishes were one of five basic types:

• wax
• oil
• varnish
• shellac
• paint

Modern chemistry has added polyurethane and catalyzed lacquer to the list of possible finishes though these could be classified as a type of varnish (more on that below). Both of these are fast drying and much harder than previous finishes. But they lack the warm and tactile feedback of earlier finishes and I rarely use them even on my modern projects (exception: table-tops).

Here we're looking at a brief overview of each finish, why and how it works. Then we'll get into how to prepare it and use it in the workshop.

Waxes

Waxes are among the most ancient of coating materials, predating written history. Traditionally, waxes came from either animal or vegetable sources. What's left you ask? Parafin, a petroleum by-product. In the British Isles wax is almost always beeswax.

Source and Preparation

Beeswax is secreted by bees for use in the construction of the honeycomb and is removed from the comb by melting it with heat. Beeswax tends to be soft with a low melting point of 60-65°C/140-149°F. Its properties can be modified somewhat with processing, though likely the extent of that was filtering and purification. It can be lightened with bleach and colored with pigments.

Once the New World was opened, Carnauba wax (also known as Brazil wax) became available. This was made from the Carnauba Palm tree, a native of Central and South America. It's one of the hardest natural waxes and by itself is too hard and brittle to make a good finish. However, add 15% or 20% Carnauba wax to Beeswax and you'll have a wax finish that is a lot more durable.

Application

The most basic application of wax is to rub solid wax over the surface to be finish and then burnish it to teh desired sheen. The mechanical and thermal action partially melts the wax and drives it into the pores of the wood.

A less labor-intensive approach is to prepare a liquid(ish) version which can be spread more easily and then buffed out. Liquifying wax involves disolving wax shavings in a solvent like turpentine or alcohol. To speed the process along, you can heat the mixture. However, I hope it's obvious that this can get pretty exciting given the low flash point of the solvents. I would not use an open flame.

The drawback to a wax finish is that it never cures into anything harder than the wax you put down. While it's water resistant, it can easily be removed by mechanical action (wear) or solvents (alcohol) and must be frequently renewed.

The Score on Wax as a Finish

Advantages

• Mildly water resistant
• Moderately resistant to acids and alkali
• Does not color the finish of the wood
• Easy and quick to apply (rub on, rub off)
• Very forgiving during application
• Easy to refresh the original finish if it becomes worn or damaged
• Non-toxic and food-safe (Once solvent has evaporated!)

Disadvantages

• Damaged by alcohol
• Must wait for underlying finish to cure completely, or solvent in wax may damage underlying finish

Recipes and Usage Notes

Go to Wax Recipes for several different recipes, how they can be used and my expericence with them (if any).

Oils

The second oldest approach to finishing wood products is the use of oils. You can use any oil, even animal fat, though that has some obvious (and odious) drawbacks. Historically the preference is for what is called drying oils. These are plant-based oils that polymerize (harden) when their fatty acids are exposed to oxygen. Linseed (flax), walnut, and poppy were the most popular sources of drying oils.

Linseed oil is still a quite common wood finish and can be purchased in most hardware and big-box stores. While you're there, in addition to cans of "Boiled Linseed Oil", you will see things labeled "Tung Oil" or "Danish Oil". These aren't made from tongues or Danes. These products almost always have linseed oil as a base with some other additives to justify the extra cost.

Linseed oil dries pretty slowly. Depending on conditions, it can take from days to weeks to fully cure. Clearly, that's a problem for the furnituremaker trying to earn a living. Luckily you can shorten the curing time by heating the oil, saturating it with oxygen, or by adding metal salts (called "driers") to the oil. Often all three are employed. The resulting Boiled Linseed Oil will dry in a few hours.

I ended up doing a deep dive on Linseed Oil and you can read All About Linseed Oil.

I have a page for Linseed Oil Recipes and use.

Varnish

Varnish was available in the Middle Ages although its first documented uses were on paintings as a final protective layer.

Theophilus Presbyter gives two recipes for making and using varnish in his early 12^th Century work De diversis artibus. His varnish recipes are basically the same (allowing for translation) as we have from post-Rennasiance authors like Andre Roubo (L'Art du Menuisier, 1769).

Cennino Cennini mentions varnish in his Il Libro dell'Arte (~1400) in the same context as Theophilus. Interestingly, he includes a recipe for making paintings look like they have been varnished. Was it an expensive issue or an availability issue?

It is not clear when it started being used on furniture. We have evidence of it being used on furniture by the sixteenth century based on images in paintings. But, we can't say if it was common, only on the highest status items, etc.

More research to come.

Other Finishes

The following are some other finishes I have found, put here for future reference. I have not experimented with any of them (yet).

Danish Soap Finish

Yeah, really, soap. Source: Caleb James. There is also some information on Chris Schwarz's Lost Art Press Blog.

One of the most mysterious things about Danish modern furniture to me when I started making it was this strange soap finish that is talked about so often. I wondered, "What is this all about"?

Well, the easy answer is that it is a soap that is simply washed onto the wood surface. You may wonder how that protects the surface, though. Basically, soaps traditionally were made of oils of some sort or another. Your grandma or great-grandma would have used "Ivory" soap flakes that were made from vegetable-based sources, palm and coconut oils usually. Everything from clothes to who knows what was washed with it.

Why use soap to protect wood surfaces? Wood has pores and those pores will get clogged with dirt and oils from use if not protected. Soap clogs those pores and keeps the dirt and oils out. Also being soap, it also releases dirt and oils easily thus keeping them off of the surface.

Wood also benefits by having a finish that slows the exchange of moisture from the wood to the surrounding atmosphere, thus keeping it more stable. Soap finishes aid in doing this like other finishes though to a lesser degree.

The biggest advantage, I believe, is that it leaves woods like white oak and ash looking as natural as the raw wood itself. As a woodworker I love the organic feel this gives a piece. The soap finish is also incredibly smooth to the touch and ages so beautifully.

Some suggest that soap finishes are a lot of maintenance. I have found that since they age nicely I really don't do anything to maintain their appearance. If it does get soiled, simply wiping the surface with a damp cloth will usually remove whatever is unwanted. Wiping the surface with more of the same soap will freshen it up as well. In Denmark, this is often used to finish floors even. I think that attests to its durability and effectiveness as a finish. I purchase my soap flakes from a U.K. based producer. www.msodistributing.com currently can supply this in the US.

Here is how I prepare my soap finish. I mix boiling water and soap flakes in equal parts, 1/1 ratio. If I am making a large batch I will reduce the water a bit. I only want enough water to dissolve the flakes and it should create a whipped cream-like consistency when mixed together but with a thicker body to it, not so airy.

First, measure out your flakes and then pour the boiling water in equal parts over the flakes. Let that sit long enough for the flakes to absorb the water and it will get a translucent appearance and will become sort of jelly-like. Now mix in a bowl until you get the consistency I mentioned above. See the photo below.

You can now place a small amount inside a lint-free white cotton cloth that is folded over itself. Squeeze the soap through the fibers and to the outer surface. This will thoroughly saturate the cloth with soap. Now wipe it on the surface of your wood. Put on enough to fill the pores. Don't let it cake on the surface, though. Once it is dry you can knock down any raised grain with 220-320 grit sandpaper. Apply one more coat and that is usually sufficient. Finish by buffing with a soft cloth if desired.

To freshen up your finish follow the same steps. If you have a set in stain you can try pouring some boiling water on the spot. The soap will often force the stain loose. Let it dry and reapply a finish.

A note of caution; Do not wet end-grain surfaces too heavily. These areas absorb more water than the face grain and can crack if continually saturated. Thus it is best to make your soap with less water and more like a paste. Also coat both sides of a panel, such as a tabletop, evenly so that it will reduce the potential to cup or warp.