Han wrote:
" wrote in
m:

Not to argue, but are you sure they are glazed? Don't look glazed in
the photo. Terra cotta tile is very soft, so you should be able to
sand the scratches with fine grit. I would put a clear glossy varnish
if you want them to look glazed - it will help conceal fine scratches
and keep water out. If you're in a cold climate, sealer might help
preserve them from water freeze/thaw.

They didn't look glazed to me either, but they do look scratched now.
Not sure how to repair that. I would suggest that they either be left
alone, or replaced.

OP probably has considered that .. suggesting simplest alternative.

As far as water freeze/thaw is concerned, most houses in Holland used to
have terracotta tiles for roofing. They last almost forever, and in
Holland it can get (occasionally) down to 0F. Winter is an almost
constant freeze-thaw.

The tiles on a windowsill will collect snow, some melt, some seepage
through porous tile, then freeze and crack. Maybe.

Of course, your terra cotta may be different from the Dutch variety. The
Dutch word for this kind of rooftile is "dakpan" (roof pan), and a google
search for "dakpannen" (the plural) should give you plenty material.

I've sanded harder ceramic stuff. Terra cotta is generally a lot softer
than other clays. Most I've seen is Mexican, but I'm no authority.
I've used latex stucco patch to fill defects in masonry (concrete
block). It would be pretty easy to use it to fill in the broken tile
and then paint with a little craft acryllic paint to match the tile.
Ours isn't exposed to freezing, but there is no sign of different
surface once painted.