I'm about to start mixing the silicone RTV compound to make the molds that we've set up.  There are several different varieties of very good quality clear silicone RTVs on the market.  The most important feature in my opinion to be looking for is the tear resistance and that will allow you to have long life out of the mold.  It will also allow you to stretch the mold as you're cutting so not to damage your master so that's one of your considerations.  The one we're going to be mixing with today is probably the one I use the most.  It's a Freeman jewel sill product.  Many of you may have seen it it used to be available in a cartridge but we were mixing it now that's how it's available.  And it's ten to one so there's ten parts of the base material and there's one part of the catalyst.  So it's a total of eleven parts.  Some people get into trouble thinking it's ten parts equally.  So it's a total again of 11 parts, 10 parts base, one part of the catalyst.  

Now we're going to have to figure out how much silicone we're going to need for the job.  So if I wanted to recreate this large mold, I would simply weigh this and that would tell me basically how much silicone and I need but it won't tell me how much I need for waste.  I generally try to figure in about fifteen percent of the silicone I mix by weight to be waste that'll be on the bowl or on the spatula or on the mixing device.  Now on the micro frames it's very easy to remember.  Just think eight, eight.  Eight grams of silicone for every one eighth inch thickness and mold frame.  So the half inch frame is going to be four eighths,  8 times 4 is going to be 32,  so I'm going to need 32 grams of silicone to make a half-inch mold frame.  Five-eighths easy enough to figure, that's five times eight that's going to be 40 grams of silicone and so on all the way up through the one and a quarter inch mold frame.  Now again that is the total of what I absolutely need to have maximum, but I'm going to have to get a percentage to add for waste.  So I'm going to add up these six molds I'm about to make and then I'm going to add fifteen percent on top of that to allow for waste.

Alright I've got six molds that I'm going to be making today that we've set up and four of these six molds are the half inch size and we've already determined that's 32 grams each.  So 4 x 32 should be about 128 you got the calculator not me.  Then I've got two that are going to be half inch those are for to each. So let's just say in round numbers we've got about 210 grams of silicone to make.  Now we're going to add fifteen percent on top of that and we can round that we don't have to be exact let's say that is another 30 grams of silicone.  So right around 240 grams of silicone is what we need to make.  So again we're trying to make our life a little bit easier with the amount of silicone we're figuring so I've come up with just dividing the total that I want roughly by 11.  So in this case I'm going to put 220 grams of the base material and I'm going to put another 22 grams of catalyst material to make our proper mixture and blend.  You can be a little off but don't be very much off at all.  Try to use a digital scale and try to remain very accurate.

So we're going to start with this scale and we're going to have the terascale open.  We're at zero now including the container and I'm going to pour the base material to again testing 220 grams.  Now it's a little thick but you'll get pretty good experience about how to cut it off.  Now the reason I'm pouring the base first is what if I run over just a little bit I might have to adjust how much catalyst I'm going to be putting in.   I can come pretty close by pouring but just in case I make a mistake I want to be able to adjust it and I want to do that on the catalyst side.  Now what we're going to try to do here is never put any material on the side of the bowl always trying to get it dead center because we don't run them run into a problem of unmixed portions of the silicone or that will make a mess when we're trying to make the mold.  

So now that we've put our 220 grams of base material in, we need to add that 11th part which is going to be the catalyst.  I actually had 223 on the scale but that's not going to mess my ratio up enough to make concern.  So I'm hitting terra to go 20 on the gram scale and I'm going to put 22 grams of the thinner catalyst material into the mixture.  I'm going to try to hit directly in the center of the base material that's already in and it's going very thin, will go very fast so do it slow, I'm going to stop at 22 grams.  Okay so I've hit my 22 grams and now we're ready to mix.  

Okay so we're now we've measured our silicone, we've got the base in the catalyst, we've got approximately 242 grams of silicone which is going to be enough to fill these frames, with a little bit left over to clean up.  So what I use and I find it's the easiest you can mix it by hand but generally the arms going to get a lot more tired than this is going to get.  So I feel that by mixing the silicone thoroughly it cross links it much better and adds to the life of the mold.  

So I'm using the timer that came in the Firefly kit.  I've set it for five minutes.  I'm going to start it now and I'm going to mix the silicone using just one blade from the cheapest mixer you can find at medium speed for five minutes.  Now this is going to add a lot of air into the mix but again we're not going to worry about it because it's going to be taking care of these bubbles while it's under pressure curing in either the NoVac unit, the Firefly unit, or the bigger silver bullet that's behind me.