Just a quick tutorial as it came up in a build.
How to make broken clay pots.
Take a resin or plastic pot, or a bead that you are using to simulate a pot and use insta-mold/blue stuff/omyaru to make a one sided mould of the top, bottom and a side.
Use milliput/aves epoxy sculpt/magic sculpt to fill the mould and take a brush handle to push it to the sides and top of the mould.
You want it thin on the sides but not too thin. If the putty is slightly translucent when holding it up to a light it is too thin.
Wait for the putty to set for 24 hours so it is completely cured. De-mould and start clipping and cutting each piece. Try to make it look like natural breaks and glue in place.
I will probably superglue some broken egg shells on this pile too just to bulk out the broken pots.