Making a Magpie

Discussion in 'Lost wax casting' started by DJN Holistic, Aug 29, 2022.

  1. Mantrid

    Mantrid Silver

    On the subject of mould making, 5kg of silicone is more than enough to mould your sculpture so long as you make it relatively thin supported by a plaster mother mould rather than a silicone block mould. I am just finishing a series of videos showing this process. I will be posting the first in the next couple of days. You might find it helpful.
     
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  2. DJN Holistic

    DJN Holistic Silver

    I have a basic idea of how to do mother moulds, but seeing a video on it would be helpful. I've got some plaster, but I don't have much thixotropic solution (enough for about 1kg). What I might do is block mould the body and do your method for the wings and tail to save on material.
     
  3. Mantrid

    Mantrid Silver

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  4. DJN Holistic

    DJN Holistic Silver

    Been a while since I updated. I found I was rushing to get to the end a bit, so I took a break which turned into procrastination. To get myself motivated again I switched to a different project for a while and started working on this.

    kangaroo.jpg

    It's a Kangaroo which I attempted to sculpt from hardware materials. Mostly it's made from cement and polyfiller. I hadn't really intended to do anything more with it it, but it inexplicable got a lot of likes on social media, so I decided to take it further. Chopping it up was a job and a half. Really had to go to town with a hacksaw and a hammer, but I got it ready for moulding.

    I tried Mantrids mould making technique. I'm a bit conflicted on the benefits of it. On the one hand, it's very cost effective. But on the other it's time consuming, messy and the cast isn't as clean as I'd like. Some of that might be a skill issue, but the length of time is a real killer for me. Each side of the mould takes three pours. The initial layer of silicone, the thixotropic layer, then the plaster, with drying times between. Given that this particular sculpt was in seven parts, that meant 21 incremental pours with 4-5 hour waiting time between each.

    Other difficulties I had was with turning the mould over to create the reverse side. Adding a clay wall to silicone doesn't work very well, as the hydrophobic nature means rather than creating a seal, the clay had to be shored up from behind and the join sealed with Vaseline. With the clay drying out and contracting over time, it felt like a recipe for disaster. Although fortunately nothing bad happened in this particular case.

    The third issue was with releasing the part from the mould. At first I was trying to create a plaster shell which enveloped the silicone, but I found the shell difficult to remove and replace, and any flexing caused it to crack. In the end I found it easier and quicker to make a silicone and plaster sandwich, which worked a lot better, but probably isn't suitable for anything with more than a two part mould.

    KangaMould.jpg

    Despite my struggles I managed to get a complete wax set of the sculpt. Due to the not so gentle disassembly of the original, it took a bit of work to get all the pieces fit together again, but nothing a bit of patience and patching wax couldn't solve. So this ones ready to be sprued up.

    kangaWax.jpg

    I can't do any casting until the weathers improved, so back to work on the magpie for now.
     
  5. Mantrid

    Mantrid Silver

    Yes it is a long process. But its much faster when you get used to it. It gives me nice accurate joins between pieces but it does require some practice. Doing thicker block type moulds will give excellent results with minimal skill but you must have deep pockets for the amount of silicone needed especially for larger pieces
     
  6. DJN Holistic

    DJN Holistic Silver

    I've started moulding the Magpie.

    Because I wasn't too keen on the clay wall method, I did a kind of hybrid mould. Basically everything the same as Mantrid's, but I used Lego to create the outer wall. Once one side was done, it was easy to flip the mould and rebuild the lego box. Made for a perfect fit with no leakage.
    8YY_XVRnTG2CYK_QYaSd2Q.jpg

    However, I did run into some issues. I didn't realise how thin some parts of tail were, so getting the wax to fill the mould was really tricky. It took me something like 15 attempts to get 3 acceptable waxes, and even then they needed quite a bit of tlc to fix up. Without a wax injector, I really need to take care with thickness in the future.

    It's also raising some flags as to how castable in bronze this part is going to be. Eyeballing it, I think it's about 4mm thick at the thinnest parts. Getting the shell to fill might not be possible. I'll try heating the shell to a glow before pouring, but that might not be enough on its own. I know flux can help, but I don't know too much about that and need to do some research on it. I've got some new slurry coming in a couple of weeks, so I'll give it a go and see how things work out, but in the worst case scenario, I might have to modify the clay sculpt and try again.

    . i_D7pXI9QjK1Fy7mHnPy6Q.jpg
     
  7. Mantrid

    Mantrid Silver

    nice use of lego.
    Bronze is much heavier than wax, if the wax filled the void bronze will easily. There should be no problen filling a 4mm space. My fan coral is only about 1mm in the thinest part an filled every time
     
  8. Mantrid

    Mantrid Silver

    What is the red dots on your wax?
    If you are able you could leave your shell in the furnace with the heat still on for pouring the metal so it dosnt cool down. Ive been doing that myself recently
     
  9. DJN Holistic

    DJN Holistic Silver

    Red dot are where I patched it up with this stuff. https://www.hswalsh.com/product/ferris-mould-wax-red-no-6-tc0132a
    It's a very nice wax for doing repair work. Once it's warmed up in your hands it's like sticky putty.

    Good idea casting directly in the furnace. I'm worried that it'll freeze before filling. A bit of narrow is okay, but this is thin all the way down. I know that when I've used 4mm sprue, they never fill past a couple of cm.

    The other issue is if I use the tail as the mounting spot, is it going to be stable while that thin, or will it wobble around and possibly break. A problem for way down the road, and I could always mount it on a rod instead.
     
  10. Mantrid

    Mantrid Silver

    I think it would depend on how much of the tail is in contact with the surface. A 4mm thick tail is more than enough to not bend under the weight of the whole sculpture. But if you only have a tiny point of it in contact with the surface it could break at that point
     
  11. DJN Holistic

    DJN Holistic Silver

    I've been experimenting with different formula for core materials recently by making hockey pucks with different ratios of plaster, brick-dust and sand. I put all the samples in a potter kiln for 12 hours at 900C to stress test them. Turns out that all the samples survived the stress test without collapsing. However I found that least crumbly was 2 part brick dust, 1 part plaster. So I think this will be my preferred core mixture going forward.

    So I put it to the test with a bronze pour, using the kangaroo head as a test piece. I pinned it in place with a couple of brass screws and shelled it up as normal. The core material worked fine. However I did get a large pocket of air trapped in one of the ears, which is a little odd because it looks to be vented well enough and it only affected one ear on a symmetrical pattern. What I think happened is as the bronze worked it's way around the core some air got trapped and had to bubble up through the molten metal. I defiantly noticed a "glug" rise from the gate as I was pouring. So in the future I think might be best to feed from the bottom when doing a hollow piece.

    KangaHead1.jpg KangaHead2.jpg

    I got some new Slurry mix as well, so it was my first time using this brand. https://www.remet.com/en/remetproduct/remasol-jus-dip/ It applied nicely, but was very viscous and a bit hard to get into all the crevices. I've been making some little talisman things for my local gallery an they have lots of indents. Even with taking a lot of time painting the slurry on with a brush to fill all the gaps, one of the two caught a huge bogey in one of it's nostrils, but the other turned out fine.

    CelticSkull1.jpg
     
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  12. Tops

    Tops Silver Banner Member

    I'd give the kangaroo a big hoop earring right through the defect and call it whimsical :)
    I am quite impressed with what the sculptural members of the forum bring for show and tell.
     
  13. Mantrid

    Mantrid Silver

    Those bird heads came out really well.
     
  14. DJN Holistic

    DJN Holistic Silver

    Cleaned it up and added a patina. BirdHeadM.jpg
     
  15. DJN Holistic

    DJN Holistic Silver

    I've been putting off working on the magpie, mainly because I was struggling to think of a way to support it on a base. I came up with this as a solution. The leafy part was a bunch of ivy I picked from the garden, imbedded in clay, then moulded in a simple relief mould. The nouveau brace was a bit of a pain to sculpt and mould, but it should support the tail and keep it from flexing. The tail slots into the groove at the rear nicely.

    I'm racking my brains to find a way to cast the base and the tail in one piece. It would really simplify things down the road if I could. Individually they seem easy enough, but it just seems a bit tricky to do together. Base.jpg BaseWithTail.jpg
     
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  16. DJN Holistic

    DJN Holistic Silver

    Base sprued and cleaned

    BaseSprueSide.jpg BaseSprueFace.jpg
     
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  17. DJN Holistic

    DJN Holistic Silver

    Cast the base today. Two minor flaws that I can see. There's a crack in the centre of the brace. No clue what caused that. And there's a little knobbly bit behind where the tail should be mounted. Both are easy fixes, so cast successful!

    Bonus pics of my low-fi wax burnout.

    BaseShell.jpg BaseBurnout.jpg BaseFire.jpg BasePrep.jpg CherrySoup.jpg BasePour.jpg BaseShelled.jpg
     
  18. DJN Holistic

    DJN Holistic Silver

    I've been thinking about what caused the crack in the centre of the brace, and I don't think it's a casting defect, but rather a crack that formed in the wax itself while I was shelling it up. Patterns can get pretty heavy when your dipping and layering sand on, and you have to grip it by the base and move it around a lot to make sure it gets coated properly. That's putting a lot of stress on the wax. I'm always a bit anxious that the gate and sprue system are going to snap off and I take extra care to ensure they are securely joined, but I'd never really considered the effect of the wax flexing and snapping like that before.
     
  19. Mantrid

    Mantrid Silver

    What is the dust bin type furnace/ Is that for firing the shell?
    Nice result.
     
  20. DJN Holistic

    DJN Holistic Silver

    That's right. It's just a garden burner lined with fire blanket. I'd like to get a better setup, but what I have works so it's not a big priority.

    Tail's up next. Trying to crack on a bit and get everything cast by the end of the month.

    TailSprue.jpg
     

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