Ceramics is a general term that can cover different types of objects made from heated clay. The two main categories are pottery and porcelain. Whatever type you have, it will need the same care and attention.
Avoid damaging your antique plates, by leaning how to clean them correctly. Use an aerosol of compressed air to remove surface dust. Wash the plate with a soft brush in warm water with a little, gentle dish washing liquid. Rinse with clean water of the same temperature. Put the plates aside to dry naturally, don't rub them dry. Never use abrasive products, such as bathroom cleaners, dishwasher powders or bleach, on ceramics.
Don't heat up cracked plates in the over. This can extend the crack, split the object altogether or open up old repairs. There are many kinds of adhesives and their use in repair of valued ceramics requires training and understanding of chemistry. If you do use adhesive at home to repair a ceramic you will probably find it seeps out. Commercial glues can easily yellow and can be difficult to remove.
Hydrogen peroxide and sterilizing preparations are sometimes recommended for cleaning ceramics but don't use them. Their ingredients can react and cause damage, including staining. Sandpaper and scalpels should not be used.
Soaking old ceramics can have hidden dangers. Old repairs could become loose, and porous pieces will absorb water that could cause future damage. If a ceramic piece has been repaired, don't use it for serving food. It could be a health hazard.