RayChii wrote:How do you clean up the uncured silicone? Can leftover silicone in plastic pots be cleaned, or must the whole thing be thrown away?
Once the material has been mixed it'll cure so whatever is left over generally gets thrown out. Silicone does bond with itself so if you pour new silicone over an old piece they will combine into one piece, the problem is that if you have any dust, impurities, or release oils left on the surface it can mess up that bond and the mold would peel apart.
It's also difficult to recycle large chunks of excess material as they are usually oddly shaped, you can cut it up into small pieces and mix it into fresh liquid but it's very tedious and time consuming. You are better off just keeping a good estimate on the volume and not over pouring by much. There's always a little bit of waste that gets left behind in the mixing cups or spilled in the pot but once are more familiar with the process you know how to estimate pretty closely so it'll be minimal.
I'm using Lego to make a box to pour the silicone into, but I'm finding that it's prone to leaks, what can I do to plug these leaks up?
It depends where you are getting your leaks, if you are using old legos that have been around since you were a kid they may not fit as tightly as newer ones and may leak from the sides. In that case you might want to order some new ones from their "pick-a-brick" section on their website which is much better than buying kits to get just a few straight pieces.
If the leaks are occurring along the bottom of the box you can use clay or a low heat gun glue to seal around the outside edges. In some cases it may just be that you need to weigh the mold box down with something so that it presses against the bottom more firmly. I usually set a small wrench on top of my mold boxes prior to pouring which helps prevent it from sliding around during the pour and also helps prevent any silicone from oozing out from the underside.
Also just make sure that once you've built the mold box that you give it a good top to bottom squeeze to make sure all the pieces are seated tightly.
When I do my own mold boxes I don't seal any of the legos, I just build the box make sure it's tight and then place it on a piece of plexi glass, weigh it down with something and there's rarely any issues with leakage. I may get a couple small drops that leak out of a corner but it's a very tiny amount and not worth worrying about. (Usually less than a 1/4 oz) You also want to make sure the bottom surface is level and flat, most mold pots are slightly rounded which leaves a gap under the mold box. Use a piece of wood or plexi glass under the box so that it has a completely flat surface to sit on.
How can I make sure I'm making the right amount of silicone? Is there anyway to estimate or measure the volume of the mold?
If you build the same size mold boxes from legos each time then you'll know how much to pour on later cast. Example, if the first ones takes 8 oz to fill then if you build the same sized mold box again you know how much it'll use.
If you want a somewhat precise measurement for a new box size you can always use uncooked rice, build an empty box then fill it with the rice. Pour the rice into a measuring cup and it'll give you an approximate volume of the mold box. Just make sure to wipe the mold box clean before you use it as any left over dust or impurities can mess up the silicone.
After you've been working with stuff for a while you'll tend to know how much material to use simply by the size of the boxes, but that takes a bit of experimenting before it kicks in.
Is there anything else I should know before I go making my next mold?
Don't be afraid to make mistakes, if something fails try your best to figure out why it didn't work out and make adjustments. When you first start casting there's a learning curve and you'll mess up lots of times, which is totally normal. Just stay positive about it, examine your process and figure out what caused things to go wrong and there's tons of how to articles on here that can help solve most problems. Things are trial and error until you hit your stride with the basics and then it becomes super easy.