u/Skarabath

Hi everyone. I need to know if anyone else has experienced this. When making a three-tone cyanotype, I notice that after the paper dries, and before applying the second negative, it has shrunk and no longer matches the negative's size. 

I create the magenta layer using matcha tea, which gives it that pinkish-brown hue. I wondered if the hot water might be the cause, but I’ve tried letting the tea cool down, and the same thing happens. The paper is Canson Montval.

I am going to try shortly to make my first duotone cyanotype with a negative. My question is if sodium percarbonate can be used instead of sodium carbonate for the yellow tone. Percarbonate is very easily found in Spain, but carbonate is not. My tests with strips give an interesting (somewhat dull) yellow tone, but I have only tested with flat images, without texture or gradients. I also tried bleach (sodium hypochlorite), but I got a very faint yellow.