You are not going to get that section in bright plus it won't form as well as black and may even crack on sharp bends.

You say it's for scroll work but surely you are not forming a whole 4M length at one go ? So what is the max length you need to work.

If you can cut down to 2m you can get a length of industrial plastic guttering with two end caps masticed on for security and nearly fill it with brick and patio cleaner from Toolstation for £8.00 a pop diluted with water 1:1 and this will fetch all the scale off in about 2 hours.