Taking Your Coals To Newcastle Idiom
I live in a town in England called Newcastle upon Tyne, and one expression here is 'to take all your coals to Newcastle'. It means, to take something somewhere, where the thing is already in abundance. Like if you were going to try and sell cars in an area where everyone already has a better model of car, you'd be taking all your coals to Newcastle, since you're taking something somewhere where it is already abundant.
WIKIPEDIA: It refers to the fact that historically, the economy of Newcastle upon Tyne in north-eastern England was heavily dependent on the distribution and sale of coal—by the time of the first known recording of the phrase in 1538, 15,000 tonnes of coal were being exported annually from the area—and therefore any attempt to sell coal to Newcastle would be doomed to failure because of the economic principle of supply and demand.
(Sorry, thats the best I can do to explain, you can try google?)
Anyway, I like to write in Dutch to help my skills, and I want to use a Dutch equivalent of this idiom (obviously not word-to-word, but having a similar meaning). I usually write simpler texts aimed at young children (obviously I dont publish, this is just to help my language, but I need to maintain the writing style) so it can't be hugely formal, it must be understandable for children.
Can anyone think of anything I could use?
CONTEXT (it's based in Norway):
A: I'm going to sell the ice! We'll be rich! (Ik zal het ijs verkopen! We zullen rijk zijn!)
B: Pfft, you are taking all your coals to Newcastle.