HOCHMA: YESHIVAT HAVERIM יְשִׁיבָה חברים – BABYLONIAN TALMUD p90

The rabbis taught: “Although the sages said it is not allowed to deposit (warm victuals) after
dark, even in such receptacles as do not increase the heat, still, if already deposited, it is
permitted to add more cover. How can this be done? R. Simeon b. Gamaliel says: “In cold
weather the covering sheet may be taken off and a blanket substituted; in warm weather the
blanket may be taken off and a sheet substituted.” Furthermore said the same: “The sages
prohibited (to deposit warm victuals) only in the same pan in which they were cooked, but if
emptied into another pan it is permitted; and there is no fear of one coming to cook (on the
Sabbath); for (the act of) emptying (the victuals) from the cooking-pan (into another) proves
(that there is no such intention).
If one deposited a pot (containing victuals) in material that may be handled on the Sabbath, and
covered it with the same, or even deposited it in non-permissible material, but covered it with
permissible, he may take out the pot and replace it; but if he deposited it in non-permissible
material and. covered it with the same, or even deposited it in permissible, but covered it with
non-permissible material, he may take out the pot, but can replace it only if the pot was but
partly covered. Otherwise, he must not replace it at all.
It is permitted to put one cooking-pan upon another, and also one earthen pot upon another, but
not an earthen pot upon a cooking-pan, or a cooking-pan upon an earthen pot. (Even on
Sabbath) the cover of a pot may be fastened down with dough (kneaded on Friday before dusk).
In the case of putting one pan or pot upon another, this may be done only to preserve the heat,
but not for the purpose of heating the upper pot by means of the lower one.
The same as it is forbidden to store warm (victuals), so it is also forbidden to store cold
(victuals) on the Sabbath; but Rabbi permitted the latter to be done. Even so is it prohibited to
chop ice on Sabbath in order to obtain cold water, but ice may be put into a vessel or a pitcher
without fear of the consequences.