I found out the hard way not to push my luck.
I was asked to build some decorative boxes for my church that needed to be ready in time for a very important day. Knowing I was going to use shellac for the finish, I allowed only one day to apply the finish—the day before the important event. After applying 3 coats, I wondered where all the blotchy, shiny spots were coming from. They would rub out momentarily with steel wool, only to reappear a short time later.
Ugh. All that careful construction and the finish made the boxes look horrible. I took them to the Woodcr
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Fortunately, there's another great thing about shellac—it's easy to remove! A little denatured alcohol dissolved all of it. So I mixed a fresh batch, applied several coats, rubbed out the finish the next morning, and had a whole 15 minutes to spare before the big event. Whew!
So how do you determine if your shellac has crossed over to the dark side? Brush some on a piece of wood. If, after 15 minutes, it's not completely dry and looks blotchy....throw-it-out!*
Do you see all of the tell-tale shiny spots at the top of my tool cabinet door?
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Yeah, I'll fix that someday.
*Dan, the finishing guru, says to put a dollup of shellac on a piece of glass, let it sit overnight, and if you can press your fingernail into it the next day, mix up a fresh batch.