Is it an art material
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Not settled by chemistry
Two identical bottles of the same medium can land differently depending on how they are sold and to whom. That should feel familiar: the cosmetic and drug line works the same way, and so does whether a product is a hazardous substance at all.
The clear cases
A decoupage medium, a craft glue and a hobby varnish sold to crafters are art materials by any reading. A sealant sold through a builders merchant to trade is a different product doing a different job.
The unclear ones are the common ones
A wood glue sold to furniture makers and to schools. A finish sold to restorers and to model makers. Most small producers sell into both, because both are their customers.
Selling into both means complying for both
The cautious and usually correct answer is to treat the product as an art material if any meaningful part of the audience is using it that way. The cost is a review you might not have strictly needed; the cost of the other error is a product mislabeled for the audience it actually reached.
Your own marketing decides it for you
A product page that shows the glue being used on a school project has said what the product is for. Intended use is read from the presentation, and the presentation is written by you.
Put the question to the toxicologist
Along with the formula. They are reviewing for chronic hazard in the context of use, so the use is part of what they need, and asking makes the classification a documented decision rather than an assumption.
Document the answer
Whatever you conclude, write down the reasoning and the date. A classification that lives only in somebody’s memory gets quietly reversed the first time the range expands.