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I have a handful of glass jars of shellac (mixed up from flakes & denatured alcohol) that are now past their expiry date. Some of the shellac is still fluid, some of them just have a tiny amount that is sort of gummy, I imagine some may have some shellac dried onto the inside of the glass. There is not a lot of it.

I would like to re-use the jars if possible. I don't believe I can pour denatured alcohol mixtures down the drain where I am. But to properly clean the jars out of all of the 'expired' shellac & avoid contamination with a new batch, I imagine I would have to buy and use even more denatured alcohol (or some other alcohol) to use as solvent, and use up more containers for depositing it at the hazardous waste facility.

Is there a simpler / less wasteful way to re-use jars that I am missing?

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    Honestly it's probably easier to just get new jars. You can pick up a dozen mason jars at the grocery store for like $10. Leave the old ones open and once the alcohol has flashed off they aren't hazardous waste anymore and you can toss them in the recycling bin. – SaSSafraS1232 Apr 4 at 21:57
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I'm a firm believer in reusing jars used in finishing as much as possible. Especially very small jars that are handy for the small amounts of mixed finish that a single project often calls for, I will often go to the trouble of cleaning and reusing them. However, if the jars are common it often isn't worth the effort to clean them.

While it sounds like it would be better for you to just get more jars since you asked about how you might reuse them efficiently here's an option. Rather than using copious amounts of denatured alcohol (which will certainly work but might be considered a waste of the solvent) you can clean using a basic or alkaline water solution.

Shellac is soluble at high pH, hence one of the common old methods of removing it relied on ammonia.

If you make up a strong solution of washing soda that should be sufficient to clean the jars of shellac residue, and it will work even better if it's warm or hot. Best to wear gloves when doing any scrubbing that may be needed1.

A caustic soda (lye) solution will most definitely work too although lye is more hazardous to use and handle, and great care should be exercised if you go this route2. And of course the aforementioned ammonia will work if you can get that cheaply where you are. Use appropriate cautions with ammonia3.

shellac... now past [its] expiry date

Just to touch on this. There are rules of thumb about when shellac should no longer be used but be guided by what you have there. Proscriptive rules about how long shellac lasts once made up into liquid form are not to be relied upon because they take no account of the variability of shellac, a natural product (that may be further processed), and varied storage conditions.

Despite how long it's supposed to last once made into a liquid different users report wildly different shelf lives for their shellacs. Shelf life differences vary based on their local conditions, the type (colour) of the shellac in question as well as the age of the flakes.

With "past its expiry date" shellac test it and see rather that toss it based on an arbitrary date. If it dries fast enough, doesn't remain soft or sticky then it's still good.


1 Because the solution will tend to de-fat your skin. If you've ever washed your hands too many times with soap you'll know what this feels like and will want to avoid a recurrence.

2 Gloves and eye protection should be considered mandatory when using lye. Read up on the dangers if not familiar with it! And something not always mentioned, be sure to use a container that can take heat — lye going into solution is an exothermic reaction and at the extreme can boil the water.

3 The fumes aren't pleasant to inhale and can sting the eyes so it may be best to work outdoors. Just to note there are still very strong solutions of ammonia available in some markets (stronger than common "household ammonia" dilution) but my advice would to be steer well clear of them for this purpose unless you know what you're doing.

  • All of those cleaning agents are soluble in water. Have a large bucket of water available to rapidly dilute any spillages - particularly lye. – Martin Bonner Apr 6 at 16:46
  • Thanks for the recommendation about re-testing shellac before tossing it. Do you recommend letting the alcohol evaporate and then cleaning the residue using this method? – Scott Hilbert Apr 8 at 1:05
  • @MartinBonner, perhaps but really not at all necessary with the washing soda or the ammonia — both can be used (as diluted for this purpose) to clean surfaces. As for the lye, if one feels the need then perhaps it would be better to have vinegar on hand rather than plain water. Although when I use caustic soda on old tools old tools I just work in a basin in the kitchen sink, so any splashes go on the stainless steel, the melamine worktop, or the tile backsplash none of which care. For the super-careful probably best to use lye outdoors on a cement or paved surface. – Graphus Apr 8 at 6:43
  • Welcome Scott. You'll definitely save on tossing some shellac that's still good this way, believe me! As for the cleaning I think I'd probably drain the jar, and then just go straight to the basin of cleaning solution. No point in letting the shellac dry. I was going to suggest swishing out the jars with a small amount of alcohol in between but actually there's no point to that either, the basic solution either works or it doesn't :-) – Graphus Apr 8 at 6:53
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If you can redisolve the shellac by adding more alcohol, do so, then pour the resulting mixture into something disposable like an aluminum pie pan or even just a big wad of paper towel. Wait for the alcohol to evaporate, then dispose of the resulting mess in the trash.

It still means throwing some stuff out, but a roll of paper towel is most likely cheaper than some new jars, and paper does grow on trees (right next to lumber).

  • Thanks for your answer, I think the two answers probably complement each other. I am curious, I assume you recommend letting the alcohol evaporate outside. Do you have any thoughts about keeping animals from getting into it? I would assume most birds, squirrels etc are smart enough not to drink it but I would prefer not to chance it. I am thinking maybe some wire mesh. – Scott Hilbert Apr 8 at 1:14
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    @ScottHilbert I wouldn't recommend letting it evaporate inside. I hadn't thought about that, but I'm sure a wire mesh cage would take care of that issue. You could set it on the deck/porch, then sit down (upwind of it) and have your favorite post-woodworking refreshment (or 2) while waiting for it to evaporate. Your presence should keep most woodland creatures at bay. Or, you could put it up high where the dog/cat can't reach it, and count on that animal to keep the critters away... ;) – FreeMan Apr 8 at 11:47

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