What kind of cement was used and you wish to remove
One part cement such as Contact Cement or Super Glues are dissolvable. Two-part Epoxies are not dissolvable and can be removed with heat or scraped / grinded down. In most cases, it is impossible to visually tell which type of cement it is.Using a sharp object, poke the old adhesive. If it is flexible, it is most likely not Epoxy and can be dissolved. If it is hard, it is most likely Epoxy or Super Glue.
How to Remove Old Adhesive From Ceramic or Pottery?
If it is Super Glue, it can be dissolved with Acetone (or nail polish remover). Before applying the Acetone make sure you do a small test on your ceramic object to verify that it will ruin your item. Acetone will instantly damage any polymer based product (paint, varnish, plastic). If your test passed, apply the Acetone on the cemented area generously following all the safety instructions for using Acetone (e.g., ventilated area, use gloves and eye protection).
If it is not Super Glue or Epoxy, use solvent such as Paint Thinners, Alcohol or Goof Off. There are more hazards when using these-- pay careful attention to the safety precautions on the labels.
If it is Two part Epoxy, heat with a heat gun or boil in water. Again, run a small test to insure the repaired item will not be damaged by water or heat. When heating the ceramic in water, do not drop the item in boiling water to avoid cracks due to thermal shock. Place to ceramic object in room temperature water and start the heating with the object in the water. After it is boiled for 2-3 minute, inspect the object to see if the cemented parts are separated. If yes, use mittens to hold the hot item and with a razor blade, while hot, remove the remaining epoxy.
If the epoxy is no breaking down with boiling water o a heat gun, a high temperature epoxy was used which leaves you with two options: 1) Fire in a kiln to 500 - 600 degree F using a very slow temperature rise program. This option should be left for professionals only. Or, 2) Grind off the high temperature epoxy using a Dremel or other grinding devices.
Old Adhesive Removal Process - Example: