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I recently got a lathe and playing around with it I've made some cups roughly the size of a shot glass. My cousin immediately wanted to buy them off me.

I haven't found any information that seems settled on whether or not there is a good finish that will hold up under exposure to alcohol. I have found some for sale which use a polyurethane finish, and I've seen shellac recommended. At the same time, I've seen a lot of information stating it doesn't work or doesn't last long.

If shellac or poly works short term, then that's fine if I just want to have them around for novelty. But I wouldn't want to sell something that would wear out quickly or start looking badly in a short amount of time.

Is there a finish that will last for a decent amount of time, like poly or shellac?

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    I think you can rule out shellac right off the bat. Alcohol is what's used to dissolve it for application and it doesn't cross-link or whatever it is that makes a material resist its original solvent after it dries. Your user would be drinking the interior shellac with the first shot of vodka, and would likely feel the outside sticky with any spillage on their fingers. I'd be thinking a two-part finish, but I'll let others with more expertise weigh in on that. You probably want to mention what wood you used. – scanny Jan 14 '17 at 5:52
  • Have you considered turning them out of something other than wood, like say Corian? – Jacob Edmond Jan 14 '17 at 15:57
  • I mostly am only able to use what we have left over from shipping at work. Lots of pine, some pieces of oak and poplar. No corian. When I have some cash... – Mike Jan 14 '17 at 20:31
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My advice would be not to make glasses out of wood so I'll put that out there right at the start.

The only sure-fire ways of waterproofing wood are to completely encase it in a film finish, or impregnate it with something waterproof. Both of these are possible at home, but you then have to worry about the food-safe aspect of whatever you're using. I don't want to overstate this since I side with the argument that nearly all finishes are safe for direct food contact once fully cured*. However, alcoholic beverages present a particular concern since of course they contain two main solvents that would be in contact with whatever you use.

and I've seen shellac recommended

o_O

Classic example of being careful of stuff you read on the Internet. I can't imagine how someone can recommend shellac for anything like this with a straight face as it is famous for reacting poorly to exposure to water and it is soluble in alcohol. It will literally be washed off the surface if used for a shot glass! Shellac isn't toxic, but still I wouldn't want to drink it in my shot.

If shellac or poly works short term, then that's fine if I just want to have them around for novelty.

A good coating of polyurethane may do you then. Just to be clear I'm referring to oil-based poly, not the waterbased kind which is a very different thing (some could work, others definitely not so best to stick with oil-based which is more of a known quantity).

You need to build a full film on the surface to ensure it is liquid-proof, so that's at minimum 3-4 coats of unthinned varnish.

Is there a finish that will last for a decent amount of time

Obviously "decent amount of time" is open-ended but for something that'll hold up longer, excluding the impregnation options which I don't know about, an epoxy coating would fit this bill. But epoxy-based finishes are not inexpensive and application can be a bit of a bear.

Wax
I don't know if you want to run a test with this and see but impregnating with wax is one of the ways traditional wood and leather drinking vessels were waterproofed in the past.

The idea is to soak the item in melted wax (you'll want to weight them down a bit so they don't float, any glass marbles in the house?) and it gets incorporated deeply into the wood as it displaces air and water. The waxy surface feel that wax will impart may be a little off-putting but waxes are famously inert and are not soluble in either water or alcohol.


*Not everyone agrees with this and some very strongly disagree (they may believe for example that no finishes are safe unless 100% natural, which is hard to reconcile with waterproofing something to hold liquid).

  • Aren't many spirts and liqueurs aged in (oak) wooden barrels for long periods of time? The only "finish" I've ever heard of was burning the inside of them. How is that possible? – martineau Jan 18 '17 at 0:21
  • @martineau Sorry not sure I understand what you're asking, is it how the barrels hold liquid? If that's it wood is essentially waterproof (there is slow loss of liquid to evaporation over the years). – Graphus Jan 18 '17 at 8:19
  • I guess what I was driving at was, is that many liquors are aged in wooden barrels, and they seem to hold-up well holding alcohol for long periods of time—so maybe a solution is to just not finish the inside of the glasses (assuming they're made of a suitable type of wood). – martineau Jan 20 '17 at 1:24
  • @martineau Ah right I see what you're saying now. Two differences of note though, the first is something mentioned in Eli Iser's response, there's exposed end grain in a turning which is absorbent as heck. The second is if the outside is finished and the inside isn't once you've wet the inside it will create a very unstable situation, probably lead to cracking. – Graphus Jan 20 '17 at 7:56
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As Graphus mentioned, finishing for water- and alcohol- proofness is difficult, especially considering the food-safe requirement. I would suggest experimenting with an unfinished shot glass. I would look into cooperage for spirits (especially wine aging barrels), which are predominantly made out of American white oak, although red cedar is also used.

However, you should note the main difference between a barrel and a turned glass - in a barrel the liquid should not encounter end-grain (especially if the staves are made from riven lumber), while in a turned glass you will have end-grain at the bottom or sides (depending on how you turn the wood). I'd turn one out of white oak and test it.

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Wooden bars (in pubs) are often finished with a layer of epoxy. It is strong, resilient, impervious to liquids, and goes on thick, so you only need one coat. You should be able to find large bottles of epoxy resin and hardener at your local hardware store.

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