The Law of Value is for commodities, not just commodities produced through the standard capitalist formula of M-C…P…C’-M’. Artisinal production of commodities, be they art or otherwise, still confront the sphere of circulation as commodities the same way commodities produced through traditional industrial production do, even if their production circuit is distince.

Artisinal production still follows in the general value calculation, it’s still produced for exchange. No surplus value is extracted from an artist that produces commodities to exchange for their necessities, but the value is still regulated around the socially necessary labor time. The Law of Value is concerned with commodity production, capital, etc, not just capitalism.

What’s unique about capitalist production is the dominance of capital, ie the ability for a capitalist to buy commodities with a sum of money, have these work together in production, then sell the produced commodities of higher value for a greater sum of money, ie M-C…P…C’-M’.

An artist that buys their own materials and tools isn’t also buying their wage labor. There’s no surplus value extracted from them, the form a part of the small handicraftsman. The law of value still applies to how their produced commodities confront the market. They practice M-C, do their own P, then convert the new C’ into M’, but usually cannot move on to reproduction on an expanded scale except perhaps in the guild format. They get their labor-power “for free.” The C that they purchase just takes the form of mp, they supply their own L. As compared with other commodities produced artisinally, they will still be regulated around the socially necessary labor time. Rates of profit tend to be high for the petite bourgeoisie, but gross profits tend to be low due to the artisinal scale.