Cement Removal

That's all it needs - A thin layer of grease should do the job.. Cling film might also be an answer.

3rd. idea try a thin coat of gelatin - it should stop the cement PoP drying fully.

GA

mold OR mould "release agent"

To clean the plates try phosphoric acid such as driveway cleaner. It might attack the aluminium so a test is required. The other option is to soak the plates in sugar solution but this is likely to be slow.

If and when the plates are clean spray with mould oil or WD40 before next pour

Not my area of expertise... however, I do know that aluminum is amphoteric (stable at neutral pH, but corrodes faster in either an acidic OR alkaline environment) and as such, is not recommended for use in applications involving the handling of cementitious materials... (just as galvanised steel should be avoided for such use).

This site has a lot of interesting tidbits regarding plaster of paris and the casting thereof.

Though mould release agents are generally fine ideas : depending upon your Long-Term goals and needs for this process , you might do well to re-think the fabrication from the ground up...(?) Can you divulge just what these dice sized articles are?

How much shrinkage is unacceptable...?

Wishing you the best~

Mold release agents are usually necessary no matter what sort of casting method you utilize. I would give serious thought to changing your form when casting such small articles. Using a urethane mold and simply using a more non-shrink cement paste ( perhaps type K Cement ) would make the whole process painless. You would have to allow more time for curing but the ease and efficiency of stripping should make this a welcome trade-off. There are lots of urethane providers out there who would gladly assist you getting the correct compound. And you could probably use it for Halloween masks. Have fun.

If your electrical oven heat is optimum, you can use one side polythene coated wrapper paper with the polythene side facing metal surface, a possible non stick surfac provision.

The other choice can be inserting glass plates in between, sikica is non stick to many adhesives. you may insert paper also in between glass and mould paste.

The other important part is the choice on your GENERAL PURPOSE adhesive, which may have affinity for metal surface, which you can coat, dry and verify. In that case change your adhesive which should least stick to metal

Pre dusting the metal plate surface with Talcum Powder prior to mould preparation should also make the removal easy.