I have always understood that it is a bad idea to run water into a hot pan--thermal shock could crack certain types of pan (cast iron) or warp others (tri-ply). But then I read some folks here talking about cooling stock rapidly by taking a copper stockpot off the stove and setting it in a sink full of ice water. This got me thinking about my morning routine.
Every morning I make oatmeal in a tin lined copper saucepan. We scoop the oats into several bowls, and I set the pan aside to cool before putting water in it to soften the remaining oats enough to sponge it away. (This issue only applies to tin-lined, because I can scour a stainless line pan without worry.) The trouble is, if I wait too long, the residue turns into oat cement and I have to go back to the stove to simmer it away. If I could scoop the simmering oats out of the pan and safely fill it right back up with warm water, this problem would disappear. So, my question is, "Is it safe to put warm water directly into a tin-lined copper saucepan that has just come off the stove at a simmer?" As a second question, "Is it unwise to cool stock by setting the simmering pot into a sink of ice water?"