Re: testing painting - is it oil or acrylic - I forgot!
Cotton ball with alcohol, rub a dub dub. If paint comes off onto the cotton ball chances are good it is acrylic. Sometimes, you can tell by taking a whiff of the painted surface. Not always a good way but if it smells of linseed oil, chances are it is oil.
You might consider writing, with a pencil, on the back of the canvas denoting what was used.
Another idea is to add a bit of nomenclature to the serial number. i. e., AC acrylic on canvas, OC, oil on canvas, kind of thing.
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