Well, well. I tried the rust remover, thank you for your encouragement! As you can see it has worked quite well. This is the first image I posted yesterday after I applied the rust remover. I like it much better now. The colour you can see around the edges of the fabric is just some silk paint that transferred from my wooden frame - I normally use it only for silk painting.
So I must experiment a little more with the rust remover. I just tied the fabric, as I would a tie dye, but it didn't work that well. I think I might try stenciling with the rust remover. That will have to wait for another day. I am going to be busy for the next few days. Will post some pictures on Sunday.