And [finally] we're away!!!

Yes, that's right — I have finally gotten to the moldmaking stage. Let me babble on and tomorrow when I have loads of free time (and hopefully some energy) I will organise the pictures I have been taking and post them as well.

[quite possibly tl;dr]

The first day was spent entirely in preparing the first ten parts for molding. This means, cutting the baseboards to size, cutting and cleaning the PVC pipe that is to become mother molds, drilling and claying up the parts and finally mixing and pouring the silicone. Except by the time Ron got back from work at 7pm I still hadn't finished claying up, and decided to stop for the night. The next day I remembered that I hadn't sealed or sprayed mold-release on the parts, and had to remove the mothermolds aka containment fields, spray and wait for that to dry.

First pour was for the hands and two pairs of feet (flat and high heeled), and the knee and elbow parts. I have bought Platinum/addition cured silicones for this project, even though it is more expensive, it is also a lot more durable, strong and supposedly doesn't shrink, or cause the casts to shrink.

Because I am good at introducing a lot of air into the silicone when I am mixing, I put all my molds in the pressurepot to cure. For the first 10 molds I was making the split block (or split cylinder) type, which is a one part mold that you cut into to get your master out. The silicones I ordered in are both hazy translucent so you can sort of see the part inside and figure out where to cut. For the record I am using SmoothOn SmoothSil 920 and Polytek Platsil 71-40. The latter I got a 20% discount on because it was old and no longer pourable, they mixed it up with some SIlicone oil for me and I have successfully mixed and poured it. We will know in 24 hrs whether or not it worked.

But I am getting ahead of myself... I started with the simplest molds to build confidence, since it's been almost a year since I first learned to mold and cast. Day two and I am using the SmoothSil 920, I had 25 minutes working time, and unfortunately made the mistake of not checking what I could fit in the pressure pot.
Because my pot is intended for painting, there is a metal tube that protrudes from the lid down to the bottom of the pot, and with the baseboard under the molds, the lid wouldn't go on at all. Rushed down to the garage to get a hacksaw and cut the tube off. However I could still not fit all the molds in, and had to leave the knees and elbows to cure on the workbench.. full of airbubbles. Four hours later it was time to open up and see what I had gotten. After getting the masters out, I mixed a batch of resin and poured everything up.. into the pot and on with the pressure. The bench-cured molds looked like they might be okay, as there was a skin of silicone against the surface of the parts. However there were bubbles all throughout the silicone, and of course by putting the whole thing under pressure, the bubbles in the silicone collapsed and made spaces where there should be none. The resulting pieces came out looking like puffer-fish. A very interesting lesson. And the good thing is that the other six parts came out really well, although I left them overnight and demolded this morning.. I was so excited I couldn't sleep, but I didn't want to open them that night in case I would face failure of some sort and get very despondent about further progress.

Today (day 3) I decided to try the other silicone and start on some of the two-part molds. Again using PVC pipe as the containment field, I picked the headcap, hips and hip shells, as well as the neck-piece from the original twigLimbs, because it is handy and functional and the old mold for it is very worn out. It's not a two part mold but that's beside the point. Platsil 71-40 is a harder silicone than the Smoothsil 920, but otherwise very similar in the mixing and pouring stages. However it has a 60 minute working time and needs 24 hrs to set. Which means that these molds will need 48 hrs because I'll have to pour the second side at some stage.. probably not tomorrow night but the next morning.

To try to conserve my expensive materials I am resolving to use some math (online calculators) to figure out how much silicone I need for each pour. This means working out the volume of the containment field and subtracting the volume of the clay and master inside, and in some cases (such as if the silicone is mixed by weight rather than by volume) multiplied by the materials specific gravity to find the weight of material needed to mix.
But first, make sure that all the molds can fit in the moldbox, which they didn't, so I cut off the last stump of the paint-sucking-upping-tube, and good riddance.. I don't know why I put up with it for so long...

Everything fitting I find my math and my scales and start mixing up the silicone. This stuff is really messy.. mixing silicone is always messy and I go through several pairs of gloves in one batch. It's also extra fun when both part A and part B are translucent and you can't tell whether they are mixed or not. With the SmoothSil I elected to just spend loads of time making sure it was mixed, and with the Platsil there was a difference in consistency from A to B so I was able to (hopefully) figure out when it was properly mixed.. but I did take my time too. Cleaning up cured silicone is easy.. it peels right off when it's cured. Uncured stuff also sets up a little but also leaves residue so no touchy without gloves, or risk sensitisation over time.
So I've left my workbench in an absolute mess, but all the molds I made are in the pot and I'll think about cleaning after I've poured their second halves on Thursday morning. Not sure what I will spend tomorrow doing.. I could clay up some more molds and get them ready, or I could clean the house.. dust bunnies are accumulating again.

Anyway, got dinner on the stove and I should go watch it, but as I said I will organise my pictures tomorrow so you can all see what the setup looks like and things might make more sense when they can be visualised.

*over & out*