Full Chisel Blog

March 22, 2010

Shellac, one of the top three finishes [again]

Filed under: Finishing,Historical Material,Of Interest,Techniques,Uncategorized — Stephen Shepherd @ 7:14 am

From Feb 4, 2010:

Shellac, one of the top three finishes
from Full Chisel Blog by Stephen Shepherd

Shellac is a particularly unusual finish with ancient origins. First used centuries ago, its initial use was as a dye stuff but then when mixed with alcohol made a fine spirit finish. Used as a substitute for real oriental lacquer, it is also a thermoplastic cement used to hold stones while grinding or for stopping, an excellent finish called French polish is extremely high gloss, the first hair spray and a food grade called ‘confectioner’s glaze’ makes candy and pastries shiny.

Lac Bug

During the 17th century in Europe it became a popular finish and the first books on its use were published. It was all imported from the east, mostly India, it is still being produced as it has been for millennia. There have been attempts to synthesize shellac but to no avail. A small [the size of an apple seed] female insect Lacca Lucifera, it flies to a fig or acacia tree, finds a suitable branch and settles in. A small needle like mouth pierces the branch of the tree and sucks out sap. It then exudes [read poops] a red sticky substance and gets stuck, where it sits and sucks and poops. At the end of the cycle, the bug lays what is reportedly a thousand eggs and dies. The youngsters hatch, dine on their dead mother then bore their way through the shellac and move on to another tree. Trees are given a few years in between the infestation to allow the trees to recuperate.

At this point the shellac is harvested by cutting of the small branches and scraping away all of the residue, mostly shellac but with some twig parts and bug parts. Stick-lac is the crudest [read unrefined] form of shellac followed by seed-lac (no stick, but still small woody parts). It is then placed in cheesecloth bags and heated over a fire until it becomes slightly liquid, the bag is twisted and the shellac is squeezed out filtering out the bug parts and twigs. It is formed into round drops called button-lac and sold in that form. Further processing by heating the shellac and pouring it over a large pottery cylinder shaped jar, then warmed in front of a fire and stretched into large thin sheets, which is broken up to make flake shellac. It can also be bleached to make a lighter colored shellac called blond.

De-waxing shellac is a popular idea at the moment and it is suggested that the naturally occurring wax interferes with modern finishes. It doesn’t seem to interfere with traditional finishes and there is little evidence that this was done traditionally. I personally think this is a waste of time and shellac, the best parts are what settle out, I always mix it up before use. I think it also contributes to a French polish finish, a simple method of applying shellac with a pad and produces an extremely high shine.

If you don’t mix up your own, which is very easy, you can also buy commercially available shellac in a can, it comes in orange or white [bleached] and is a fine finish providing it is thinned at least 50% with alcohol. Alcohol is the only solvent for shellac, although it will melt at high temperature. There is a standard called X pound cut, indicating the [X] number of pounds of shellac per gallon of alcohol. Three pound cut being common, it is way too thick to use and must be thinned. Several thinner coats are much better than one thick coat. I have no idea of the pound cut of the shellac I use but I imagine it is around a quarter pound cut, meaning one quarter pound of shellac to one gallon of alcohol and this works fine for me.

Shellac is reversible, so it is great for restoration work, it is all natural and comes from a renewable resource and is non toxic, although the denatured alcohol is, I use pure straight grain alcohol, just in case. It is easy to use and if you mess up it can be removed. Pigments can be added to the shellac to make a glaze and I even make fast drying paint by adding more pigments. Shellac is a great finish for woodworking and among the top three woodworking finishes.

Again I would like to thank Michael D. for saving the original posts that mysteriously vanished.

Stephen

2 Comments »

  1. Hi Steven,

    Can you discuss, or have you already in a previous post, your application techniques?
    Up to now I have had no problem with either a brush or rag applying the first coat or two of Zinzer from a can thinned 50%. They are thin and easily sanded level. It is in the subsequent coats where I encounter problems because it seems to dry faster and leave a pretty uneven surface.

    Best,

    Tico

    Comment by Tico Vogt — March 22, 2010 @ 10:57 am

  2. Tico,

    Welcome, I have discussed shellac a few times and a search will give you those posts.

    As to multiple applications of shellac, because it solves itself subsequent coats can cause the previous layers to soften leaving an uneven surface. I generally apply a couple of thin coats, sanding between coats, then I will French polish the shellac to a high shine. I also thin the subsequent coats and put them on very thin and don’t work the surface, just lay on a thin coat of shellac. Or I isolate the layers by applying a mixture of linseed oil and turpentine 50/50 and wipe off ALL excess and allow to dry for 24 hours. This prevents the next coat from effecting the shellac as it has a thin coat of dried linseed oil.

    Hope that helps.

    Stephen

    Comment by Stephen Shepherd — March 23, 2010 @ 9:44 am

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