Moldmaking Mold making preparation and questions

HI - I am not sure what flumo is, but if it is anything like sculpy, I only coat the master with mr surfacer to see where I need to sand the outside, I dont put anything on the inside. That is, I could have them uncoated (the sculpy master) and do a mould in silicon and not have any problems with porosity.

 

I think the general consensus is that La Doll, Premier, DAS, and other air-dry clays need to be thoroughly sealed before using them as masters to make a plaster slip casting mold.

Furthermore, there is a chance that you can lose the air-dry clay master, even though it has been thoroughly sealed. I have heard of this happening on at least one occasion to one doll maker.

As with anything else that you are not quite sure about, please make a test plaster mold on a test air-dry clay part before committing your original doll sculpts to the process.

What you will probably experience is that the first few coats of sealer will be absorbed by the porous air-dry clay. Once the pores of the air-dry clay have been completely filled with sealer, and have dried, will a coat of sealer stay on the surface.

While I have not used any air-dry clay products myself, I do have experience making plaster masters to make plaster molds. Plaster is also very porous. I usually used orange shellac as a sealer, and applied many coats due to the plaster absorbing the first few coats. Then I used a soap/water parting agent.

 

If you want to mold a porous master you have to coat it first, yes. My doll is made of airdry clay and I used mr. Surfacer (many, MANY layers, because it also helps you to make the doll absolutely smooth) on both the outside and inside surface. Others have used gesso and that seems to work as well.
So yes, to avoid trouble molding the hollow parts I did coat the inside of the pieces as well - best as I could. The shafts of the arms and legs are too narrow though, so I just made sure I sealed them off with NSP clay when I molded them (you will have to do that anyway, otherwise the silicone will get everywhere)

I did have a few problems with coating the pieces, though and have just recently discovered what it was. When molding, complete areas of the mr. surfacer were just torn off, basically ruining the mold (because each cast would show these cracks) and the master to some extent. I first thought that the silicone would attach itself to the coating somehow, but now I know the real reason.

With some of my parts, air was trapped between the coat and the clay, resulting in blisters you can't see with your eye, but when pressurized, they crack or burst open. I'm not sure what caused it, but am recoating parts of the master now to fix it.
Telling you this, because you can hear something's off if you tap with your fingernail on a blister. The sound the coat makes is different from the rest. If that's the case; tear it off and start over. It will save you a lot of money.

I hope this helps you a bit.

 

silk: I gather that you are pressurizing your silicon molds when you make them?

 

I would steer clear of Torkworks, I have personal experience with them and the quality of their doll casting work is not good. They are good at doing their own stuff, but for dolls they don't understand customers needs and they don't want to put the time and effort in to get it absolutely right.

 

Yeah, I pressurize both the silicon and the resin. Gives (if done right) perfect bubble-free casts.

 

Maybe you find this blog useful:
http://rico824.blog101.fc2.com/blog-category-9.html
She made Ladoll master and coat it with layers of wax and then create the plaster molds.
Try with test pieces, I think it could work.