When I first entered the level, level 4 or 5 I think, it gave me a message about it being warm on the level. The entire time, I stayed at warm and didn't take any warming food or extra clothes. I did have a cursed linnen hat on though. I spent most of my time exploring the level, and making sacrifices to the goddess in hope of getting my cursed hat off of me. It wasn't until I decided to leave the level that within just a few turns, I went from warm, to hot, to boiling, to dead.
I don't think cursed items have anything to do with temperature. You just can't take them off, and they deteriorate more quickly. My guess is that the warm level is what caused it, although I haven't seen this happen within a few turns.
I put a crude bronze breast plate that I had crafted on the alter. I didn't notice any difference between before or after I put the armor on the alter.
Did you actually 'u'se the altar? Simply dropping a piece of armor on the altar doesn't work. You should see a message like 'the runes on the altar disappear' if you used it correctly. Also, did you wear the armor after putting it on the altar? There may be no apparent change to an item until you equip it.
(It isn't always obvious how to use dungeon features. I sometimes make the mistake to pray '_' at a shrine in stead of 'u'sing it, for example.)
[Edit: I just ran into one of these things, and it's called a 'stand covered in fresh blood', not an altar. When used, the description says 'The engravings have disappeared', not runes. Also, it made my main weapon 'harmless'.
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