I had a problem recently with masking fluid that wouldn’t come off my paper.
I’ve been producing a series of Jacobean flower inspired paintings. Part of my process is to mask off certain parts of the painting to help keep the images light.
We’ve had some extremely hot days so far in our summer down here in Oz, and I think it affected the fluid. I use Winsor & Newton, normally without a problem, but this time it went sticky, changed colour and wouldnt rub off the watercolour paper. I was using a heavy 300gsm rough paper, (Saunders I think).