Is there a general creative % mark-up used in the trade for
Probably not, because you would need to know the total number of
pieces sold in advance. That would be the only way to recover the
cost of your creative work.
And here you have the itch “cost of creative work”. Actually,
creativity is not a cost factor, it’s probably the reason people buy
your stuff. If you want to recover the 12 hours to make the master,
then I would probably split the costs over the first 50 or 100
pieces sold. After that, this cost share is becoming extra profit.
Still, I am having a hard moment to understand creativity as a cost
component. I have an artist friend who once explained how he sets
his prices: It is the amount of money that relieves enough pain to
separate him and the object; a kind of separation allowance, if you
price = cost + markup is only giving the lowest baseline possible,
sort of security belt to avoid you losing money. After that, lift
your prices as much as you can. You will eventually find that you
sell less, but at the same or better profit while working less.