How to make a two piece mould from silicone rubber
This is one of the most basic silicone rubber moulds. Its called a two piece mould because (yep you guessed it) it has two pieces, a top and a bottom.
To make your mould you will need a few things, they are:
Lego bricks or other construction type brick and a Lego or other construction type plate to build your mould walls
Something with a blunt point for pushing plasticine around
Silicone rubber and curing agent
Non important object to use as mould funnel
A container for mixing your rubber in
Something to stir your rubber and curing agent together
NOTE: I will not give mixing quantities as you may not use the same brand of rubber as me and I don't want to mess up your mould. all mixing quantities should be taken from the products YOU use.
First select the item you wish to make a mould of, then embed half of it in plasticine.Look at the item you want to mould and determine if this is the right type of mould for the object as some objects may need a 3,4 or 5 piece mould (I'll cover them in a future "How to..." ). I recommend putting a small amount around the object first.
Now build a box using the Lego or other construction type bricks build the box twice as high as the embedded item to allow for the rubber. next place the item with the plasticine round it into the bottom of the box and fill out the rest of the bottom half of the box and insert your non important object to be used as funnel object and push two divots into opposite corners using the end of a paintbrush so your mould will aline at the end. you can put globs of plasticine over any gaps on the outside of the box you think the rubber will seep through. for the most part Lego or other construction type brick is quite a tight fit.It should now look something like this.
You are now ready to mix up your rubber. I used this silicone rubber by Trylon as it comes with a curing agent.
A good way to tell how much rubber you will need is if you pour water in to the area you want to fill with rubber, then pour the water in to a measuring jug or baby cup with a measure on the side if it's for a small mould. Remember to dry the mould properly after you do this as it could ruin the mould making process.
Once mixed leave the rubber to settle for about 10 mins, to admire your work so far, make tea and to let any air bubbles you have created while mixing rise to the surface and pop.
Now you will need to coat the plasticine with a Vaseline to stop the rubber sticking, I tend to use a small paint brush that I paint miniatures with. It must be a very thin coating of Vaseline so you don't loose any detail and to make sure your mould is still a tight fit for casting.
It's now time to pore the rubber. Pore the rubber in from a single corner and let it slowly work its way round the item working its way round and in to all the little nooks and crannies.
once this is done you should put it some ware to dry it will probably take 16 to 24 hours to dry so find something to do for a bit. Might I recommend the new series of Dr Who?
16 to 24 hrs have now passed, your rubber should now be set, give it a prod with your finger to check.
Remove the Lego or other construction type brick around the area that is plasticine and then carefully remove the plasticine leaving the object you are moulding in the rubber. Now put the Lego or other construction type pieces back in place, but put the plate on the bottom covering the rubber filled side this time. It should now look something like this.
Now make more rubber and pour it in to filling this half of the mould. You shouldn't need to use any more Vaseline but if you spot a dry bit the feel free to use some.
Again wait 16 to24 hrs for curing, then remove all Lego or other construction type bricks and you should be left with this.
Pluck the excess rubber of it if you want, there will probably be a bit ware it has seeped in between the bricks. Now the fun part. CAREFULLY separate the two halves of the mould and remove the object and TA DA! A two piece mould that looks somewhat like this.
Hope this will be of some use to you guys and gals. If there is a bit I could have explained better or something else just drop be a comment an I'll answer as best I can
Next time I'll be doing a "How to...." make a cast from this mould.
Future posts will include how to make and cast from a one piece latex mould.