Suitable Spirit for Varnish-Making

When making spirit varnishes for polishing furniture etc., the gums and resins (colophony, sandarac and shellac etc.) are dissolved in ethyl alcohol (ethanol) – or more acceptably, for safety reasons these days – Industrial Methylated Spirit (IMS or ‘meths’). Meths is also known in some parts as denatured alcohol (DNA).

Aside from the added denaturants that make methylated spirit unpalatable, meths purchased from hardware shops or supermarkets may legally contain up to 43% water as well. Water is miscible with alcohol and is a profitable means of cutting meths without greatly affecting its usefulness for most domestic purposes.

Any spirit that won’t, or is slow to dissolve shellac, almost certainly contains a detrimental percentage of water. It is prudent to read the labels on meths containers to ascertain if the contents have been adulterated with water and, if so, to what degree. Newly bought spirit labelled as being 95% or greater purity will dissolve good quality, fresh shellac quite adequately.

The age-old method of testing spirit’s fitness for varnish-making is quite straightforward:

Rectified Spirits are made from Wine, or Sugar, or Mault Liquors; or from Cyder, Perry or Moloſſos; or from the common Spirits made of thoſe things by Rectification. They are for the Diſſolution of Roſins or Gum Roſins and therefore if not highly rectified, are unprofitable for theſe Uſes.

Now, to know whether your Spirit is good or no, you muſt put ſome of it into a Spoon, and put a little Gun-pouder to it; then ſet the Spirit on Fire, if it burns all away and fires the Gun-pouder after it, it is good, and will diſſolve your Gums; otherwiſe, not.[i]

(Hence the term gunpowder-proof or ‘proof’ used to describe alcohol content.)

Not nearly as good fun as proving meths with gunpowder, but equally efficacious, is this simple method: Pour a little meths into a container, add a few drops of mineral turpentine and then slosh it around. If the contents remain clear, the meths is perfectly all right, but if it turns cloudy, the meths contains an undesirable quantity of water and is only good for cleaning one’s spectacles.

Jack Plane

[i] William Salmon, Polygraphice, or, The Arts of Drawing, Engraving, Etching, Limning, Painting, Vernishing, Japaning, Gilding, &c., eighth edition, A. and J. Churchill, and John Nicholson, London, 1701, p. 857.

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About Jack Plane

Formerly from the UK, Jack is a retired antiques dealer and self-taught woodworker, now living in Australia.
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13 Responses to Suitable Spirit for Varnish-Making

  1. Brian Lowery says:

    Diethyl ether can also be used as a solvent for shellac. I used it to “French polish” a turning while it was on a lathe in the late 60’s. You could buy ether back then very easily. It is probably a “controlled substance today and might not be easy to get. It evaporates and therefore dries much quicker than alcohol based shellac, but be careful. Some people will pass out at the smell of ether.

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    • Jack Plane says:

      Now you’re getting into aetheris spiritus compositus territory – commonly known as Hoffmann’s Drops. It was partaken of in much the same way as The Green Fairy (absinthe) was by weak-minded socialites.

      Diethyl ether is an NMDA receptor antagonist, creating a euphoric state which probably isn’t the most responsible state to be in while finishing furniture.

      JP

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      • Brian Lowery says:

        The reason for using ether as a solvent is to speed drying. When applying on a lathe that is spinning the object, the surface is dry by the time the object stops spinning. Plus, you can apply many more coats in the same time as alcohol based shellac would take. It really works.

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  2. Andrew Nolan says:

    I think that ethyl alcohol is much safer than methyl, the latter will make you blind and kill you whereas the former will make you drunk. In Australia metho is ethyl alcohol with colouring and a bittering agent added to it.

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    • Jack Plane says:

      Alcoholic beverages contain ethyl alcohol and you are correct, methyl alcohol is nasty stuff, but a small amount is added to meths (hence ‘methylated’ spirit) as a deterrent to those who would drink the stuff.

      JP

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  3. Doc Scantlin says:

    Isopropyl Rubbing Alcohol contains water but is cheap and devoid of many of the harmful chemicals found in hardware store alcohols. To get the water out, simply add salt. The salt mixes with the water and not the alcohol so you have a nice pure layer of alcohol on top of a layer of saline/water solution. Note also, some states are watering down their liquor store “pure” alcohol products.

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    • Jack Plane says:

      ‘Salting’ alcohol is an age-old practice that involves adding a desiccant, Epsom salt (magnesium sulphate), which readily absorbs its own weight in water.

      If I had a 20 litre drum of suspect meths I might consider salting it, but frankly, I would rather spend my time more profitably elsewhere and just purchase fresh >95% spirit.

      JP

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  4. Dan Brown says:

    I use 190 proof grain alcohol from the liquor store. no poisonous substances and if things are not going well, I can just drink a little. Has worked well but would appreciate your thoughts on it.

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  5. FIG Woodworks says:

    Always wondered how to tell if my meths was fresh, think I will take a tea spoon some matches and gunpowder with me to Bunnings next time I am looking for supplies to mix up some polish

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  6. Scott says:

    Now I have a valid reason when my wife next asks what I am doing with that bottle of liquor and container of gunpowder. Thanks Jack.

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  7. Sylvain says:

    Denatured alcohol exists for tax reasons.
    In Belgium there are accises on drinkable alcohol (ethanol). About 25 Euro on one liter of pure (100%) alcohol. So on a “cheap” bottle of 0.7l of William Lawson Whisky at 40% you pay about 7 euro accises, then you add the production cost, distribution cost and benefit and then you add 21% value added tax on top. Total price 13.35 Euro of which about 9.3 Euro of taxes and accises. There not much left for the production of the whisky itself.
    For denatured alcohol you would not pay the accises and I think the VAT must be 6%.

    Sylvain

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