Oyumaru

おゆまる Oyumaru is a Japanese non-toxic children’s toy thermoplastic. It comes in clear, coloured or even sparkly bars. It has a flexible rubbery consistency that goes soft when put into hot water and has a remarkable ability to catch detail. Upon returning to room-temperature it regains its firm but flexible consistency. I have not come across anything that the Oyumaru sticks to, this makes it ideal for making moulds. No need for vaselines or any other chemicals or tools to make the cast release from the mould. In this hobby it has loads of applications from replicating textures to duplicating a bits. If you no longer have use of your mould you can reuse the Oyumaru by simply putting it back into hot water and it will go soft and malleable again, ready to be reshaped and to take on new details.

You might know it as blue stuff. Marketed to hobbyist by Green Stuff World. I do like Green stuff world, but I am torn by their practices of just repackaging and slapping a hefty price tag on things.

When I bought my Oyumaru in 2017, it was very cheap compared to what Green Stuff World was pricing Blue Stuff at, even though the Oyumaru I bought was repackaged for the west with english packaging.

Looking at the price difference today it seems to have levelled out a bit but that might have to do with brexit and other things, so depending on where you live the difference might be more or less severe. For me in the uk oyumaru is still a bit cheaper.

I have been using green stuff or Milliput epoxy to fill my moulds. I've never used liquid resin to cast things but I do not think it would be the best to try with this since I think it heats up while curing so it might cause the mould to lose details.

I have seen some people making a frame for the mould and a lid so they can apply even pressure closing the mould. I have not gone to those lengths but maybe it might improve the output quality but I cannot speak to that.

Above: I came across a very versatile and useful wooden platform from the "Warp Lightning Cannon / Plagueclaw Catapult" that was a very useful size for a lot of projects. I made a mould of the piece and I added a wooden dowel to help align the two parts. 

You can make your own one part mould or two part mould. If you make two part mould the hard part is to fill the mould with the right amount of epoxy. Too little and the details will not be filled in. Too much and you will get distortion and mould line problems. I have gotten around this problem by mainly using it to cast parts where it does not matter much the thickness or if I get a mould line. 

Here you can see the cast platform I made, from my previous post on pump wagons. Once having replicated it, it’s easy to carve the epoxy/greenstuff to the right size. If there is a bit of warping when the epoxy sets, that adds to the adhoc quality of green skin engineering.

To make four pump wagons for my Snotling Blood Bowl Teams I needed a certain amount of plank boarding. Above you can see that some details have not quite come through, and this was actually intentional. I didn't fill the deepest parts of the mould since I knew I would need to fit a wheel axel and some other bits underneath. I didn't want protruding details that I would have to cut off once cast.

The piece in situ.  More pictures in the post

Used again for the bottom of another pump wagon. Very versatile and and doesn't make it obvious that it is the same piece. Just a rugged knackered and nicked wooden platform.

I wanted proper old school demon claws for my Chaos Dwarfs with the claw mutation. I had an old metal Daemonette so I wrapped her claws and made a mould. 

Blood Bowl Chaos Dwarf with Claw mutation. Only blue-tacked on but you get the point. More pictures.

It is a very useful versatile tool to have in your tool arsenal. You won't use it for every project but when you do, it won't fail you and you'll be impressed with how well it works.