Addition-cure silicones use a platinum catalyst that is easily poisoned. A wrong colour paste can leave a surface tacky or uncured.
What inhibits platinum
Sulphur compounds, amines and amides, tin compounds (from condensation-cure silicones), and some organic pigments and plasticisers can bind to the catalyst. Even traces on mixing tools or moulds can cause problems.
Choosing a paste
- Use pastes in a silicone carrier, so nothing incompatible is added
- Choose pigments known to be free of inhibiting groups
- Keep paste additions within the recommended level
Shop-floor rules
Keep tools and containers for addition-cure separate from condensation-cure work, avoid latex gloves (some contain sulphur) and run a small cure test whenever you change paste, batch or silicone.
