molding a fish head

[oldyellowdog]

walleye, open mouth open gills.  I was looking to cut the tongue where the gill rakers start, and where they meet the inside top of mouth.  then building a dam around the mouth, and pouring rubber inside , with the gill cover up. then turning over, when cured, and pouring over the outside of the head, with a dam around the head. anyone ever done this?  is there some unforeseen problems?  any suggestions? is it best to freeze the head?  mold max 20, or dragon skin? with dragon skin, should I do a thinner coat, say 1/4 in. then a mother mold? will it stretch better for under cuts? should I cut the teeth of first? what will be the best way to fill the mold?  Dan

[oldyellowdog]

anything??

[Mostly Fantasy]

I wouldn't thin dragon skin, as it's pretty thin (not viscous) to start with, and thinning will cut down your tear strength.  Your approach sounds "sound", just be sure to coat any exposed silicone from the first pour with vaseline/mold separator before pouring the second silicone.

[CrabCrazy]

all the info you want, is here on the smooth-on site   


 http://www.smooth-on.com/    

[Doug Bridges]

Dog,
Your method will work. Or maybe I should say "should" work.
I think for internals like a fish mouth, any good silicone will work for you. You may want to look at the "elongation before break" value on the material that you chose. This will give you an idea of how much stretch you will get from the silicone before it breaks. MoldMax 20 is at %520 and Dragon Skin at %1000. I think both are good choices.
Another thing to consider is the material. Mold Max is a tin based silicone and Dragon Skin a platinum based.
Pros: Tin
less cost, more resistant to chemicals that cause inhibition (or cause the silicone not to cure)
Cons: Tin
finished molds don't last very long, maybe 6-8 months on the shelf, lower tear strength, 10 to 1 mix ratio requires a scale
Pros: Platinum
long mold life, 2 to 3 times that of tin, most have high tear strength, most are a 1 to 1 mix ratio by volume
Cons: Platinum
Higher cost $2 to $3 more per pound of material, less resistant to inhibition mainly sulfur (If you have hard water with sulfur content, your water will cause inhibition)
I also think you will just need to pour a full plug. If you are trying to build a thin wall on an interior vertical surface, you will not be able to keep the material from running back down. You can thicken both materials, but I would just go with a full pour.

[Doug Bridges]

Another thought.
You can look at MoldMax 10T. The T is for translucent. You can use ThiVex for thickening this as well as most other of the Smooth-On silicones. It has a high tear strength, more than the standard mold max. So with this material, you can thicken it and then brush it into the interior of the fish and build the wall. Then you can create your hard plug to keep the form of the mold when casting.

There are so many ways to skin this cat. Pick one and go with it and try it out.