Materials Spotlight: Shellac

Like Hide Glue, shellac  is another “natural” substance, the use of which is traditional in this industry and has been sanctified by time.

While it is undeniably interesting and fun stuff, it’s also just as sticky and messy as glue, so we don’t want to get too playful with it!

In player piano actions, its primary use is as a sealant. It sticks to absolutely everything, which is good if you put it only where you are supposed to! As the carrier solvent evaporates, the shellac slowly cures to a hard shell. It can be made in various concentrations to suit the purpose required.

light-yellow-shellac
dried shellac flakes

A standard lighter body concentration is a 2 pound cut, which is 2 pounds of shellac flakes dissolved in one gallon of solvent of denatured alcohol*. If you need to finish a piece of wood with a light finish, it can be a good historically informed choice.

Medium body shellac (4-6 lb cut) can be “painted” inside of block channels to seal the wood pores against air leaks. This is what was used in factory production.

Thick shellac (as the name suggests) is simply a very thick formulation. Also called “burnt shellac”,  it’s great to reinforce a fastened joint, which can’t be glued but still need strength. An example of this would be for the arm flanges of a motor. The flanges attach to the bellows with small screws, but as they are under a constant load, they need a little extra strength as insurance. However it’s not a good idea to glue them (as they may need to be removed for repair purposes), so shellac is a good compromise. It can also be used around the junction of metal bits into wooden blocks, etc. Once cured it is airtight like the sealant, and won’t come off, unless you want it to. And here again, it is wonderfully “undoable” like hide glue. After it is completely cured, it is brittle and can be chipped away if it needs to be replaced.

This wonder substance of thick shellac can be made in two ways: additive or subtractive. Note that the finished product is not exactly the same in both cases, as explained in further detail here.

The additive way is slower, but safer. Buy yourself a bag of shellac flakes (from a woodworking supply store), and gradually add a minimal amount of solvent, just enough to dissolve the flakes. If you can get it right you will have a thick goopy mixture.
If the flakes are not mixing completely with the solvent after a long soak, try moderate heat. I put my jar in an (empty) electric glue pot for half an hour and it really did the trick!

The subtractive way is the traditional way, as the other name suggests. Premixed shellac is bought from the hardware store, then “burned off” by lighting the liquid on fire, and letting it burn for such time as that it thickens to a goopy mixture. It will cool to a thicker consistency than that which it burns, so don’t overdo it with the burn off!

Burning shellac to thicken

For this method it is highly recommended that you do this out of doors away from combustible surroundings.

Disclaimer: I take no responsibility for any cataclysmic events that occur after the reading of this post!

*for some strange regulatory reasons, denatured alcohol is not commonly available in my jurisdiction of Canada. One can substitute methanol (methyl hydrate, easily found), however it is important to realize that methanol has a higher volatility and evaporation rate, and the fumes apparently contain a higher toxicity level than denatured alcohol. It is not recommended to use methyl hydrate without proper ventilation; an approved and rated respirator mask will help you err on the side of safety, which is a very good thing!

A specialty woodworking or chemical vendor should be able to supply proper denatured alcohol, or another appropriate product. For example, Lee Valley has a shellac thinner on offer, which although not the most cost effective, can work well if need be.
Do your homework and shop around!

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