ANUBIS head Feedback on my molding partline and silicone choice.

[FreddySchramm]

Would love some opinions on my molding process from the think tank.

I'm planning on molding this Wed clay sculpt using a brush on silicone. (Hoping to get a very long life out of this mold) Im going to crystal clear it beforehand. As far as my part line goes, I'm thinking of jewel cutting a slit along The back and below the chin exactly where I marked in the photo tomake it easier to demold like a glove and invert. Any opinions?

Another thing, there's two silicon paths I can go, mold Max 30 or rebound 25.
By default I was going to use mold Max 30 since I've used it many times before as a universal silicone, just not on a particular shape like this. I had mold Max 30 in mind when I was choosing where to jewl cut the mold. Id prefer to use mold Max 30 because I'd be able to pour it all over the clay sculpt and it will easily flow into all of the pour detail of without using a brush too much to disturb the first layer.
In comparison, I'm thinking I could use rebound 25 instead because it's more stretchy than mold max 30 so it will more than likely last longer given my suggested partline location. However, Ive never used this particular silicone before. What I've seen online is it's very viscous, so I can't necessarily pour it on like I would with mold Max. I'm afraid when I brush it on it will disturb my clay sculpture and not necessarily pick up all the pour detail or even worse push it down and deform the clay as I brush. Another downside would be because this is so flexible, I'm afraid the mold might sag a bit if I make it too thin, since I'm so used to the rigidity of mold Max 30. But I could probably combat this by just making a hell of amount of keys and strategically placing them.

Either way, Im planning on reinforcing the mold with some spandex all over, especially a strip above my jewel cut line.
What do you think of my jewel cut placement, and what are your opinions on the silicone?

 

[udog]

As for shelf life a platinum silicone mold(Rebound or others) will be more durable than a Tin Silicone (Mold Max). Tin deteriorates faster along time, not sure if platinum even does. Also platinum will last a bit longer when casting certain materials like PU resins and it´s shrinkage is negligilbe. Tin does shrink a little.
What will be the casting material?
The part line could work. But you will always be at risk of the silicone tearing where the parting line ends. So, yes, it would be good to reinforce at least that area with some kind of mesh. But could end tearing anyway depending on the stress when demolding.
If you go for the parting line that way it would also be a good idea to create a thicker shape along that parting line (when brushing the silicone) in order to achieve a shape that fits in the shell mold when the silicone is cut. This will keep the silicone in place in that area, if not you might get problems in the seam, being as thin as the rest of the mold it might not want to keep in place.
There are many different silicones out there. Rebound is already thixotropic (thickened) but you can find others that can be thickened with chemical thickeners (for example DgSkin series+Thi Vex), and play with other shore harndness and viscosity.

 

[FreddySchramm]

As for shelf life a platinum silicone mold(Rebound or others) will be more durable than a Tin Silicone (Mold Max). Tin deteriorates faster along time, not sure if platinum even does. Also platinum will last a bit longer when casting certain materials like PU resins and it´s shrinkage is negligilbe. Tin does shrink a little.
What will be the casting material?
The part line could work. But you will always be at risk of the silicone tearing where the parting line ends. So, yes, it would be good to reinforce at least that area with some kind of mesh. But could end tearing anyway depending on the stress when demolding.
If you go for the parting line that way it would also be a good idea to create a thicker shape along that parting line (when brushing the silicone) in order to achieve a shape that fits in the shell mold when the silicone is cut. This will keep the silicone in place in that area, if not you might get problems in the seam, being as thin as the rest of the mold it might not want to keep in place.
There are many different silicones out there. Rebound is already thixotropic (thickened) but you can find others that can be thickened with chemical thickeners (for example DgSkin series+Thi Vex), and play with other shore harndness and viscosity.

Just so I'm on the same page with what you're saying. Is this what you're trying to describe when you're talking about creating a thicker shape along the parting line? Making a giant stripe on top of the build up silicone And then cut into that?

 

[udog]

Just so I'm on the same page with what you're saying. Is this what you're trying to describe when you're talking about creating a thicker shape along the parting line? Making a giant stripe on top of the build up silicone And then cut into that?View attachment 1422358

Exactly that.

 

[udog]

Take care you do that right after your general silicone last layer is starting to kick, or at least don´t let a day pass. Silicone might not bond one to another.

 

[FreddySchramm]

Take care you do that right after your general silicone last layer is starting to kick, or at least don´t let a day pass. Silicone might not bond one to another.

Really? I've always been under their impression that silicone will stick to silicone Even if the bottom layer has already cured fully.

 

[udog]

I've always been under their impression that silicone will stick to silicone Even if the bottom layer has already cured fully.

Yes and no. Silicone does bond to silicone, but if it has been fully cured for too long it can peel off like a banana skin, seen this so many times. In fact to aid adhesion over an older cured silicone sometimes it´s necessary to use heptane so the silicone swells and opens the pore.
Take in account it´s not only the silicone itself, but also any grease you might have left with your hands and most important, microdust, which is everywhere floating unless you´re in a white room.
Also softer silicones might bond better after cured than harder ones.
I have many tin brush up molds here, If I pick one of them and try peeling layers I laid on in different colors most probably I will delaminate them. Have done that test.
Also mechanical adhesion is not the same as chemical adhesion. Sometimes layers may look bonded, but it´s just a mechanical adhesion. It grabs to the texture below.
I´m talking about layers brushed from one day to another.

 

[Shoguno]

Yes silicone don't bond with other silicones.. I tried it once to repair a broken mold of Mold Max 30... the mold was fully cured since a week or 2 and tried to pour in some silicone calking on it see if it would repair the mold, but no. For a head sculpt like your anubis i would certainly do like udog said and use REBOND 25 like you use for other under shell coat molds. It is very rare that it will alter your sculptures and not take all the details, Platinum silicone is the Saint Graal for mold makers these days.

 

[Shoguno]

After that i would use polyurethane or epoxy with fiber glass to make the shell...

 

[FreddySchramm]

Well it ended up working out.