Ishkur Cinderhat:
Following the Q&A section of Chaos Dwarf Radio Ep.2, and several messages that were sent to me with questions about mould making and resin casting, I’ve made a short - but hopefully exhaustive - tutorial.
Note - this is my personal take on making two-part moulds. There are many other ways to pull a mould and many other materials available. See the Useful Hobby Links in this section of the forum for alternative ways.
PART I - Mould Making
[1] What you need: mould-making silicone (regular bathroom / sanitary silicone will not do) a clean plastic cup to mix the silicone, some plasticine / modelling clay (something that will stay soft and not harden if exposed to air), tools, LEGO stones and a release agent. Read the instructions that come with the chemicals!
[2] Now we create the first half of the mould. Embed your sculpts in the plasticine about halfway. You want to make sure that no silicone will go underneath the pieces - the sculpt would be trapped in the silicone. Use the LEGO blocks to define the size and shape of the mould. You can use other stuff as well, but I found LEGO is easy to use, flexible and re-useable. Press some small plugholes into the plasticene.
[3] Cover the whole thing with release agent and leave to dry. Put some on the LEGO blocks as well, the mould will come off more easily then once it’s hardened.
[4] Prepare the silicone. I use RTV (room-temperature vulcanizing) silicone rubber. The advantage of this material is that you don’t need to heat it or apply pressure to get the vulcanization (i.e. hardening) of the rubber going. The product shown is a simple to use two-part mould making silicone. Other products on the market are one part only where you add a specific amount of a chemical catalyst, usually some drops of special liquid that comes with the set. This is tricky for small quantities of silicone. Imagine you need 2 spoons of material, and then you’re supposed to add between 3-6% of the catalyst! The two-part silicone is simply mixed in a ratio of 1:1 and then gently stirred for about 1 minute. Try to not have too much air bubbles in it.
[5] Pour the silicone into the mould form. Small amounts at first, so that no air is trapped between the green and the silicone, then the rest. Take heart, you will see your precious sculpt again! 
Knock at the table a few times, to help trapped air get to the surface. Then leave the piece to harden. Note that some silicone types will harden quicker in a warm area.
[6] Remove the lego blocks. The plasticene should generally come of quite neatly. Scrape off small residue where necessary. I use an old toothbrush to gently clean up the whole thing with some water. Voilà, you have 50% of your mould!
[7] Rebuild the mould shape with lego blocks. Make sure your greens stay neatly inside the mould and have not come out anywhere. Cover the whole thing with mould release agent again and leave to dry. The mould release is very important at this stage. If you forget it, the next layer of silicone will completely combine with the first one.
Repeat steps [4] and [5]. Remove the LEGO and gently pull the two mould halves apart.
[8] This is the final result. You have your original greens, save and unharmed, ready to be archived. And you have your two-part mould to replicate them as often as you want. Note the plugs that have formed where you pushed the plugholes into the plasticene. These will help to make sure that the two mould halves will align properly.
Part II ‘Casting’ to follow in the next days.
Pyro Stick:
Thanks for this! It should come in very handy. Cant wait for the next part. Now i just need to find the mould making silicone. Where did you buy your supplies ishkur? Ebay doesnt seem to be very good although i did find this shop on ebay that people might find useful:
Mould Making and Casting Supplies
Would you recommend anything that they sell?
edit: I found the silocne that you are using here for anyone that is interested:
http://www.zhermack.com/Industrial/Mould_making/prodotti/ZA_22_Mould.kl
Can you buy this at their site ishkur?
Hashut’s Blessing:
That makes sense and is so simple. Now, I gotta make something worth replicating 
Thank you greatly, Ishkur. This is invaluable information. By which I mean uber, not suckish.
WarplockMonkey:
WOOOOOOH!
FINALLY someones made a thing showing how to do this!
Does it work well Ishkur? What about with thin peices?
Ghrask Dragh:
Great stuff Ishkur mate, much appreciated too.
Thank You
:cheers
Kera foehunter:
thats so great!!!Ishkur i personal want to thank you one day im going to try that
thanks kera
Canix:
Great stuff i will have to try some shields for my second wolfboyz unit :cheers jsut neeed to get the bits now:hat
Hammerhand:
Thanks ishkur, I’m going to try this soon. Just one question, where do you pour the resin in?
Xander:
Bravo!! Very well done. I await part 2!
Ishkur Cinderhat:
Hehe great, people! No go and expand your Chaos Dwarf forces tenfold with casts of your greens! 
I buy my resins and silicones here, and I am quite happy with the brand. I’m sure you can get the same brand from other online shops (which might be closer to your place) as well.
@WarplockMonkey: it also works for quite delicate pieces, you just need to be a bit more careful. I think the horns of the bull heads on these shoulder pads are quite thin already, and they came out nicely:
Knight Of Awsome:
YAY!
I’m going to fallow the same steps when i make my bull centaurs.Whats the brown stuff that you use for a base that you model your green stuff over?
Nice job:cheers
torn:
fantastic.my first 2 part mold i forgot step 7 (adding the mold release) but all my materials are labelled in german (i have same mold release) so i got a bit confused.
one thing i have been doing is using a flat lego base plate to make a more solid mold box.
also . . i wish my rubber was that fancy blue colour i only have a boring dark red!
GRNDL:
One tip I can add to the mix is to not pour the rubber directly onto the model, but off to the side and let the rubber “roll” over the master. This way, air won’t be trapped under the poured rubber but gently pushed out when the rubber rolls over it. It won’t get rid of all the trapped air but helps a lot.
Also, you can make a cheap “vacuum” bed by placing the master and freshly poured rubber into a larger box, put the whole thing into a plastic bag and then put the nose of a hand held vacuum into the bag. Use your hand or an elastic band to seal the bag around vacuum and switch it in for 10 seconds or so. This will form a negative pressure within the bag and encourage the air bubbles to rise to the surface of the rubber.
dedwrekka:
One tip I can add to the mix is to not pour the rubber directly onto the model, but off to the side and let the rubber "roll" over the master. This way, air won't be trapped under the poured rubber but gently pushed out when the rubber rolls over it. It won't get rid of all the trapped air but helps a lot.
Also, you can make a cheap "vacuum" bed by placing the master and freshly poured rubber into a larger box, put the whole thing into a plastic bag and then put the nose of a hand held vacuum into the bag. Use your hand or an elastic band to seal the bag around vacuum and switch it in for 10 seconds or so. This will form a negative pressure within the bag and encourage the air bubbles to rise to the surface of the rubber.
GRNDL
I've seen the same thing done with a commercial vacuum sealer you can buy at many market places (Wal-Mart and Target in the US, no idea about other countries). Using a home vacuum sounds like the more economic option though.
A great article!
A bit on making the cast with the new two-part mould would be excellent for those doing their first cast.
Narflung:
Well chap, you’ve done it again, good work. I have always been interested in the larger scale (ie whole mini) moulds, I’ve been doing a much smaller scale version for details and embellishments for some time, but was unsure how to expand into larger moulds.
Cheers
Ishkur Cinderhat:
That’s a cool idea GRNDL, I was already wondering how one could simulate a vaccuum-chamber for improving the mould quality. I’ll definitely try this out! :hat off
torn:
One tip I can add to the mix is to not pour the rubber directly onto the model, but off to the side and let the rubber "roll" over the master. This way, air won't be trapped under the poured rubber but gently pushed out when the rubber rolls over it. It won't get rid of all the trapped air but helps a lot.
GRNDL
i usually brush a thin first layer of rubber on to make sure it gets into all the gaps
Sharp:
Ishkur, a question for you. I happened to try my hand at casting this weekend and I ran into a small problem - Cleanup. I’m using the same 2 part silicone as you are (my bottles say 6 hours to set though) and I’m having a hard time cleaning up after. I’ve realized that the container I mix the actual silicone in is a write off, but I also have graduated plastic cups that I use to measure the materials in. Together these compounds are almost impossible to clean, but even separate they are a pain in the ass. The only conclusion I’ve come to is to wipe out the cups the best I can and label them so I only use them to measure the same material again (since I cant completely clean them.)
And in case your wondering, let the first half of your mold cure completely before taking it out to do the second half. Jello Rubber doesn’t hold it’s shape that well… hahaha.
Xander:
I will most likely being sculpting my own torsos for my BBs, and then casting those. My experiment was my GH5 entry in which I sculpted the entire torso, except the nose. It came out alright, so I figure I can work on a few great torso sculpts then cast them.
GRNDL:
That's a cool idea GRNDL, I was already wondering how one could simulate a vaccuum-chamber for improving the mould quality. I'll definitely try this out! :hat off
Ishkur Cinderhat
It works well for the rubber, but I haven't tried it with the resin casting. I have my doubts that unless you have a good vacuum going throughout the process, as early as possible, then the chance of pulling air bubbles out of the resin is rather low.
If you feel you've seen improvements, let me know.
Thank you greatly, Ishkur. This is invaluable information. By which I mean uber, not suckish.