Yes, the clay peels out very easily once I actually manage to separate the mold from the sculpture.
Ok, no release issues then I´d say.
I run into the biggest issue when I sculpt and mold a half mask on a 3d head armature.
The breakage usually happens when I make a mold on a 3d armature
All of the molds I've attempted have been half-molds. Half masks, faces, etc
For what I read I assume we are talking about a one part mold.
Could it be you are facing some kind of locking or slight locking there?
How thick is the clay you laid over the 3d armature?.
Sometimes the armature shape could be locking the mold. If the clay you added on top is too thin in certain areas or if the seam or end flange of the mold locks with some part of the armature. Sounds like something similar could be going on.
Yes, fixing something on the armature that aids leverage would help. But take in account the strength employed to open a mold is a big deal though it might not look like so. So it must be a very sturdy fix.
In any case remember slow repetitive movement to get air in will make more that one straight strong pull.
The other thing to take in account is why are your molds breaking. What plaster are you using?. Are your mix and proportions correct?. How thick are the molds?. How do you mix and prepare your plaster?. If not done correctly it can result in more brittle material.
Plaster molds must be at least 2-3 cm thick (better 3 in your case) in a general basis and with no reinforcement.
Stone plaster (like UC30) would be a strong option if you are having problems. Reinforcing your molds with burlap helps too.
Also, you must let the plaster set completely. Sometimes opening too soon can result in cracking. In your case, as it seem to be hard to get it out, let it sit 24h.
If you are having this problem one thing to do is to go for stronger molds.
I considered sticking the armature with the sculpture and mold intact into a 5 gallon bucket of water for a bit, but I didn't know if that would cause issues with either the details inside the mold, or if the moisture would stop the plaster from curing all the way. I made the mistake with one of my earlier sculpts of adding water to the outside of the mold while it was curing to smooth it out, and it never fully hardened after that.
What I said about filling with water would apply on a two part mold. Not sure it would help that much in your case.
Anyway, if a plaster mold is fully hardened (lets´s say 12h-24h) there´s no problem wetting them. This is, if the proportions and mix are correct. When using water based clay the best way of cleaning is with water and a brush or similar (done this hundreds of times). So nothing wrong should happen, unless the plaster is not well done.
One way of knowing your plaster has set and is prepared for demolding or cleaing etc. is when it has cooled down. Plaster heats in the hardening reaction. When it cools down it has set, the main reaction is over. This doesn´t mean it has dried totally (this can take weeks). But you can then work with it.
In the case you mention, trying to smooth out the surface with water (something that can be done), I´d say that the plaster wasn´t in the propper stage for doing so, or you used too much water or the plaster was not ok.