I had some rubber casting supplies left over from a project last spring. What I wondered was if it would respond well to thermochromatic ink. And yes, I discovered, it works very well. The mix I used was about 1/2 tsp red, 1/4 tsp blue and an equal mix of part A and part B of the silicone rubber casting goo- about 4tbsp worth.
Mix well. Use gloves and be in a well-ventilated area. I poured the mix into the lids of three small cups and laid the stainless steel thread into the goo.
When cured (6hrs), the rubber was nicely reactive to temperature. However the thread I laid into the mix had become too resistive in the rubber and would not conduct enough to heat the matrix. To solve this, I sewed some stainless steel thread into the rubber. This solved the issue and worked quite well.