Shellac is never useless Mark . From small drawers to large antique cabinets it's a lovely and rewarding material to work with.
Yes, there are many varieties of flaked shellac, from the most common raw which may even contain pitch, to low wax, to wax free, which is clearer and more resistant to humidity. To remove wax from shellac dilute in alcohol 50% leaving it a week, then seep with paper filters.
Well that question got me googling...
There is a lot of discussion about this on the ”interweb”, but mostly in relation to woodworking and nail polish!
Shellac is a natural product, subjected to various purification processes prior to sale which have changed significantly over the years, so firstly, the shellac we buy today is likely to be much purer and more consistent than in the past.
Shellac flakes sold for making wood finishes definitely deteriorate with age. After a period of time the can no longer be dissolved in alcohol. I haven’t found out exactly why, but moisture, heat and light are all cited as causes. So, keeping your flakes in a sealed dark container would be a good thing.
Shellac in stick form will have a lower surface area for a given volume and therefore certainly less susceptible to moisture.
Once mixed with alcohol, shellac will start to react chemically, (search for esterification if you want to know more), and evaporation of the alcohol doesn’t get you back to where you started. This is why pre-mixed shellac varnishes have a short shelf life.
Shellac is chemically similar to acrylic, and hence made of long polymer chains. I’ve read conflicting information about whether these will cross-link in ultraviolet light (the process that causes unbreakable watch crystals to go yellow and brittle). However, I would expect it to behave in a similar way - again, this is a non reversible reaction.
All of this may go some way to explain why some people reprt there is no problem with cleaning pallets in alcohol and others saying it softens the shellac.
I’m now into this deep enough to need a good chemist to get me back out. Any volunteers?