Kelly's Studio: First casting…

Well I did it! I wasn’t sure I would, but I got a cost of the broodmare out in time for the show on Saturday!

Here she is! Please note, I have some reworking to do on the neck and pastern/hooves:

I’ll talk more about the reworking required in my next post, I wanted to document the process and why and wherefores of this model first though.

The reason I like to document these processes, even though it may become perhaps a little tedious for those of you who subscribe to this blog, is in the hopes that these little mini-session may be of some use to those just starting out in this field, just as blogs I’ve subscribed to, such as Lesli Kathman’s Blackberry Lane Pottery blog have been to me. Without this post and the series following it I would not have had the confidence to cast Very Little One myself and probably wouldn’t have taken on casting the broodmare myself either! Having these posts does allow me to look back and see whether I’ve improved my processes or am falling into the same old traps too, so I hope you will indulge me on these long step-by-step posts.

We left off at the point where I had just removed the original model from the waste mold:

Now, if you recall, I had to remove the acrylic base so my mold doesn’t have an overflow chamber for the resin to expand into as it is vacuumed. The way I worked around this is as follows:

Yep, that’s plain old simple clear packing tape! I use clear for visibility and because the brown stuff tends to transfer the brown colour onto things, but it doesn’t really matter that much. This isn’t done normally as you’d have to reapply the tape for each cast, but as a work-around it does pretty well.

Now, I didn’t get any photos of the resin being mixed or poured, or vacuumed, this is because the resin starts to cure in about a minute so I don’t have time to get shots. So, I mixed up some resin and added black pigment – I’ll explain why later. I wasn’t sure how much resin the model would need so I mixed up 100ml. I poured most of the resin into the mold and them placed both the mold and the mixing cup containing the remaining resin into the vacuum chamber and set it vacuuming. The resin bubbled up out of the mold as the air inside expanded, then the frothy mix collapsed back down telling me that the air was expelled, then it got another 30 seconds to ensure the air was out and then I very gently turned down the vacuum so that the overflowed resin could fall back into the mold without taking too many bubbles with it. I then removed the mold from the chamber and topped it up with the extra resin that was also vacuumed.

Which brings us to this image. Here we have the mold and the resin which is the black liquid that you can see has overflown during the vacuuming. I have scraped away the extra resin from the top of the mold so that I don’t have to grind away too much from the hooves, simply as I’m short on time. You can see here that the resin is very black.

“Normal” white resin (normally from Smooth-On’s Smooth-Cast 300 range) starts out clear, then as it cures it turns white. This means that, if you want a grey model, you add one drop of black pigment (for example). If you wanted a black model, you’d probably need more like four drops. Here you can see in the mixing pot how the resin is slowly turning from jet black to grey as the resin tries to cure from clear to white.

This colour change is very handy – it allows you to work out when the resin has cured. It’s always best to remove a cast from a mold when it is still very slightly flexible, so I watch very carefully to try to work out when the resin has cured enough, but not too much.

Why grey? – several reasons – white resin takes poor photographs, especially in poor lighting like during the night when I mostly work. My main reason though is that the Apoxie Sculpt I will be using to tweak this model comes in neutral (light beige) and silver, and the silver colour is very close to the grey resin. As you saw with the original model, when it is all patchy is is very hard to work out whether proportions and details are correct, so having resin and clay that match allows resculpting that doesn’t obscure the view of the model. Ok, back to the casting…

Resin is a bit of a pain – it cures in the larges areas first. This means that on first glance you might think a model is cured, but the small extremities like ears and nostrils (which are never the bits you can see) may not have cured yet. You can see this below – the resin in the mixing pot, which is about 1cm deep has cured and is a mid-grey, but the resin on the surface of the mold which is only a thin skin, is still a jet black so at this point I know that the belly of the model (the largest part) will have started curing, but the small extremities will still be liquid.

To prove this point, I turn over the mixing pot and then you can see that the area at the bottom of the pot has not yet cured (this isn’t due to not mixing enough, it is because there is a raised ridge at the base of the pot - it went on to cure fully).

Even thought the resin starts to cure very quickly, those thin sections can take up to half an hour to cure enough for demolding. Here you can see that a little while later the resin on the top of the mold has almost cured.

To test my own theory, I remove the overflow first as this is disposable so doesn’t matter if it breaks or is still gooey. Here you can see the flexibility it still has, this is a good point to demold as it has all turned from black to grey, but is still quite bendy.

The first peep – hello little lady!

I couldn’t take photos of the demolding as it took both hands and once started you can’t stop as the mold may spring back and damage the model in this vulnerable state. Demolding is very tricky as you can only flex the resin so much before it breaks or stretches, this is controlled with a multi-piece mold but with a block mold (ie one piece) like this, there is a fair bit of flexing and pulling to get the model out.

So, here is the model fresh from the mold!

These photos aren't totally accurate as the wide-angle of my camera distorts the images, normally I spend a while planning out much better photos but in this case I had to just take some snap-shots: