I just hvent been doing enough naked women lately

Ive done a two part video of my mould making process thats shows it much better than photos could. I will also post a few photos here later of the finished mould and the wax casting from it.

 

Says the video is private

 

Yes its still uploading. try again in 30 mins

 

Making videos takes as long as doing the mould making

 

Getting the silicone mix wrong was painful. Happened to me before. It's possible to add more catalyst after pouring. It doesn't really fix the pour, but it makes it easier to clean off. I use a digital scale when mixing, rather than fluid measurement as I find it a bit more accurate.

What kind of plaster were you using? I've tried this before with plaster of Paris, but I found it too fragile.

I didn't see you use a thixotropic? Were you just pushing the silicone back over the model as it set? If so, that technique is very dependant on the brand of silicone as they all have unique setting times and viscosity. I can see issues happening with overhangs too on certain patterns. Silicone is flexible enough, but depending on the shape, you might need varying thickness of silicone so the mother mould doesn't catch anywhere. An example in the picture shows how the indent in the visor had to be built up to create a shape that would allow the mother mould to separate. There is some stuff you can buy called "silicone putty" which is exact what it sounds like, a putty you can press into the indents prior to the silicon pour which bonds to the mould. Never tried it myself though.

 

I poured and wiped off as much as I could and then brushed on some catalyst to set the remainder, then peeled it off.

This is the plaster I used (they have a good selection)
https://specialplasters.co.uk/plasters/fine-plus-casting-plaster.html

When making larger moulds reinforce with bandage or any kind of fibrous stuff
https://specialplasters.co.uk/woven-fibrous-products.html

I used thixo on the second layer to thicken the mould particulaly in the undercuts. Video doesnt show some of the process as battery ran out while filming and another occasion I filled the memory card.

I save old silicone moulds and cut it up in chunks to use for bulking up. Saves money and recycling is always a good thing.

 

I've ordered some of that plaster, so I'll give this method a go.

I've been on quite a journey with different methods of making moulds.

I started by doing something similar to this, burying the model in clay to the seamline, then making a cardboard box around the edge held in place with hot glue. Once cured, I'd flip it over, reverse the cardboard wall, and pour the second half of the mould. It worked ok, but it was only good for doing two part moulds and the cardboard never quite fit right after reversing it.

When it became necessary to make moulds with more than two parts, I started filling hollows with plasticine, casting two part moulds, then removing the sections of plasticine and pouring inserts that could be removed. While it worked well enough, I was getting some horrible seamlines from the plasticine flexing the model. It wasn't a suitable method for moulding soft models either as it would damage the clay original while the moulding process was ongoing. Okay for hard stuff though like polymer, epoxy, resin prints, etc.

Next I tried using thixotropic. I'd coat the entire model in a layer of silicone. Wait for it to cure and score where the seamlines would be. I'd insert plastic shims into the score marks and then add more silicone and a plaster shell to hold it all together. Probably the best way to do large pieces, but it's too fiddly and time consuming for small stuff.

Currently I'm doing cut blocks. Dead simple and gets good results. Create a clay base and attach the model to it by the sprues and vents. Build a box out of Lego. Pour. Once its cured, follow the vents as a guideline and cut it apart with a scalpel. It sounds tricky, but it really isn't. A pair of medical forceps to hold the mould open while you cut helps a lot. Best thing is you get no seamlines or flashing and it's watertight as you don't need to cut it into pieces. Downside is it uses a lot of silicone as it's always cube shaped.

 

Yes block moulds super expensive for anything large. This sculpture took about 1/2 kg. Which works out at a resonable £12.
That plaster is good in that you can put it on thick and it doesnt run off. But if you tap it repeatedly with the back of a spoon it sort of fluidizes and spreads and flows nicely into any dimples you cut in the clay

 

This is the second part of a series of videos showing the process of making a multi part silicone mould with supporting plaster mother mould. These moulds I use to cast wax patterns for producing bronze sculptures by the lost wax method and ceramic shell.
Theres going to be three parts now not two.

 

Completed mould




Moud Opened up



I have been experimenting with this mould to get the best even thickness casts. Unfortunately the wax doesnt stick to the sharp edges. I tried initially to pain on the wax on the edges before casting but the wax I use although excellent for taking detail is hard and pulls away from the flexible mould at any slight movement. As a result when I pour rest of wax in it flows under the wax Ive painted on and doesnt merge seamlessly.

So Ive been trying a variety of soft waxes painted onto the sharp edges which are softer and have lower melting points than the green casting wax I use. Results look promising they stick to the mould well without coming off and the lower melting point means they fuse seamlessly with the poured in wax.

Ive just got to choose one now and fine tune the process to get the best result.



From left to right
Green casting wax (painted on in the problem areas only)
Victory brown
Copper sculpting wax (81 degrees C) very soft and doesnt take detail well
Art cast (63 degrees C)

 

A bit hard to tell from a picture, but 2 and 4 seem the cleanest.

 

yes thats correct. two is good but its very soft. touching it will deform any delicate detailing. 4 is also soft but not as soft as 2. Three was very difficult to get to stick and solidified quickly so by time you applied next brush stroke it would not merge seamlessly with the first. I may have another go because it was much firmer than the other two.
I dont really like messing around with different waxes in one mould so I will also try different pouring techniques with just the green wax. Im thinking to pour a very hot to get into all the detail. Tip it out and let it totally solidify in the mould and cool. Then pour the second layer much cooler and thicker. I hope that the very fine layer of wax on the sharp edges will be enough to grab and hold the thicker cooler wax.
I will experiment more tomorrow. Fortunately in the leg and knee area I can get a paint brush inside to thicken it up after demoulding. But the other problem area at the neck and shoulders cant be reached.

 

thanks Kelly. I hope to do more casting as I have more time now

 

Hope so. Theres not enough of us on the forum

 

Sprued up ready for shell. I decided to cast this in two halves so that I can completely remove the shell from the insde. Dont know what the white haze is on the wax but its not affecting the detail so I didnt worry about it.

The thing broke off the pouring cup as I was cleaning it and smashed beyond repair so the next one you see having shell applied is different to this one. Lesson learnt, make sure your pouring cup is welded properly to your sprue.

 

Try this stuff for joining wax. Works a treat. https://www.hswalsh.com/product/ferris-sticky-wax-sticks-tc0164

 

Being that size I would think she could be poured solid and avoid going through all the work of welding.

 

I have some somewhere but have never used it. Ive always just welded it all together weth a soldering iron and wax tools heated in a spirit burner. Normally its fine but I was just slacking that day