What is a good finish for shot glasses?

Question

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?

Answer 1

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.

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*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).

Answer 2

Osmo top oil is food grade safe, and claims to be impervious to "beer, wine, saliva, and milk"... but interestingly did not mention alcohol. I also have a wood shot glass to finish, so I tested a piece of wood with two coats of osmo oil by letting a puddle of tequila sit on it for 30 mins... no effect on the wood, and the tequila just rolled off.

Answer 3

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.

Answer 4

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.