A pack of Pro-Create modeling putty - http://www.kraftmark.biz/kraft.procreate.html
It comes in a practical plastic box with lid.
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As you can see it comes in two wrapped bars - one is the resin and one the hardener.
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So I gave it a try and took two even amounts of each and mixed them just like GS.
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First impression?
GREAT!
It is softer than GS, so you may have to adjust your sculpting and modeling procedures, but is really easy to work with.
Here I started with the boots for the Ogryn.
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The putty smoothens really nicely and is longer formable than GS, which is getting hard - not cured, just hard to form - rather quick.
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Next I worked on a kind of powerfist or at least armored fist for the left hand.
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it allready has some scars and scratches - I will still have to add rivets and stuff, but actually I'm pretty satisfied with this stage.