Vetting two mould process for ODST helmet.

[Southerly]

Hello there!

I am in the process of pepping an ODST Helljumper helmet, and I've had a thought about the moulding process.
My idea is to use a two-stage moulding process for the best possible finished product.

I would finish pepping the model and then seal/reinforce this on the inside. I would then make a silicon mould of the imperfect helmet prior to any sanding.
Cast a solid plaster bust of this mould, and use THAT for sanding/sculpting. This way, if I sand off too much or otherwise mess it up, I can simply cast another bust of the original model.
Once I am happy with the plaster bust's finish, then I can make a silicone mould of that to roto cast the final helmet with.

Am I completely out of my mind?

I am planning on using Smooth-On products either way. And where I am I can only buy them in large sizes (one gallon), so I should have enough material regardless.
As a side note, does anyone have a final word on using Smooth-On 300 vs 320 for roto casting?

 

[PlanetAlexander]

Welcome to the 405th! To begin with, I don't think you're mad for making a cheap mold/cast before doing a final one, this happens in the prop making industry. It's up to you if you want to put the time and money into it. Although, I'm not sure how casting plaster would go, I'm not sure how much detail it would capture.
I've used Smooth-On 300 to cast masks before, and while it works, what I have learnt is to do it in more but smaller batches to avoid pooling. Pooling occurs when there's too much resin in one spot which heats up and sets quickly. Because of this it doesn't evenly spread and sets into a chunk. Here is a page that compares the two products, although it says their cure time is the same, so I wouldn't know which is better for roto-casting.

 

[Southerly]

Hi there,

Thanks for the reply. I was going to get back to you sooner but got busy sorry. I am definitely going to do the two moulds now and I think plaster will work well, but will figure something out if not. And thanks for the smooth on advice. Will look back into more once the moulds are made.

Finally finished the pep for the helmet last night too, so here's a pic.