Bismuth (again)

Maybe there was air trapped inside when you poured the bismuth?

That's exactly what I've thought, and why I've thought (since reading replies) that either spinning the mold or pressing solid metal piece into the hole for compression would be a good idea.

Basically I'm asking if I'm going to get a volcano like before, when (I assume) the heat of the molten bismuth interacted with the vaseline and started shooting little bits of bismuth out of the hole. Vaseline was used to coat the molds, both when I was making the second mold half (so it wouldn't stick to the first) and in order that bismuth wouldn't seep through the space between the two mold halves. I assume it volcano'd because petroleum jelly is flammable (isn't it?) and I was going to use bar soap or Dawn or something otherwise.

This is a close-up of the egg btw

Thanks again for being so helpful guys, I didn't think anyone would even respond.

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Was the egg otherwise satisfactory despite the lumpy exterior? You could fill in any interior gaps with wax or something and then dip the whole thing in molten bismuth. Then melt out the wax and polish the exterior.

I suspect that whatever you end up doing you're going to have to some polishing of the exterior

That's a great idea. I may have to do it in more than two stages, but it would work for sure. I might even get a better looking egg if small crystals grow on the outside!

Maybe try a high viscosity vacuum grease instead of vaseline?

You should ask this on /diy/

Well, that's the thing. As all bismuth-geode tutorials say, you have to drain the mold before it just plain out solidifies. Bismuth crystals DO grow inside, but if you don't drain it, it just dries into a smooth metal surface . You can't see the inside of the egg from that picture, but it's basically full almost to the top, where the crack is.

So it's a lot of guesswork, because I have to drain the mold without knowing what it looks like on the inside, except maybe with a flashlight.

It's true I'll have to polish the exterior, but that will be the case when there's too much stuff on the outside rather than too little.

I'll look into that, thanks!

Yeah, I didn't realize there was a /diy/ before I posted the first of these two threads, so I just thought I would continue it here. If I post again I'll do it there. Y'all have given me a lot of good ideas.

Bear witness to this - Veeky Forums is helpful for once

Hello OP, /matsci/ here. You just got yourself into one of the greatest problems of the solder industry, the hardships of making pure Bi reference materials for spectroscopy.
The problem with bismuth is it is more dense in liquid as in solid, more like water ice. So when it solidifies it is trying to push the liquid out instead like with aluminium sucking in at the top of the mold.
Also it's crystal formation is different from the ones like Al, Sn or Fe. Bi forms a macrocrystalline structure, with the individual grains growing up to 1-3cm diameter, also it likes to form straight edges instead of dendrites or small spherical grains. That is why it will push on itself and try to push the grains apart forming big holes in it's structure, that is what you see on the top half.
To regulate the crystal formation you must regulate temperature, either keep the temp high while casting so it doesn't start solidifying during casting or you keep high temp while casting then supercool it with dry ice to make it form small grains.
Or you can ditch the egg casting thing and make nice pendants with dipping the tip of a copper wire in the liquid and wait till a single big crystal forms and just take it out of the liquid Bi.
Also you can ditch the pure Bi crystalline lines and use ~54% Sn 46% Bi eutectic alloy and cast a smooth egg like you would cast a lead or tin figurine.

Don't use soap as a lubricant, but use something less combustible than vaseline. Consider mineral oil, if vacuum grease ends up not working out for you.

cool idea.

looks like a silver ballsack. I hope you're proud

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You might try heating the mold before pouring, and also try soot from a greasy flame to coat the insides of the mold before putting them together. Silver bullets do the same thing as your egg, unless you preheat the mold and funnel and also lube the insides of the mold with carbon. You might also try graphite, just a thought.

I appreciate the help. I basically have an idea of what I'm going to do: I'm going to lube up the mold halves with something non-combustible, seal them together with woodworking clamps, pour the bismuth in through a stainless steel funnel, quickly put a ghetto aluminum foil "stopper" in the hole, then keep the cast in motion for a while until I think enough time has passed for crystals to grow, at which point I'll drain the cast back into the cooking pot. And if it doesn't look right, I'll just melt it down and try again; It didn't damage the cast at all last time I did it.

I'm afraid I can't do anything but this bismuth egg. I'm absolutely obsessed by thoughts of it. Thank you for the suggestions, though.

I will probably use mineral oil, very easy to obtain. I actually may not even need a lube with the woodworking clamps and the "locks"

Thanks, although it's not entirely mine. I know that eggs like I am trying to make already exist, I just don't know how they were made. Using a plaster cast is the best I can do.

I had thought about preheating the mold, but I was afraid the first time to put it in an oven or something. I guess I can just suspend it over a gas flame, as I already know that it can stand the heat of molten bismuth.

P.S. Where would I find the kind of soot/carbon I would use? Any better way than making a greasy fire and collecting residue?

honestly i think you might be better off posting on Veeky Forums, i doubt /diy/ knows shit about metalworking

get a pencil and scribble all over the inside of the mold

Jeweler here. When casting metal into something like plaster of paris and not a proper investment, try coating the inside of the mold in talcum powder. It helps break the surface tension of the metal until the skin solidifies.

You might not think it would make a difference but it really does. This method also helps if you're casting into a high temp silicone.

"Pure" bismuth acts different. It's not like any "normal" metal like aluminium, lead, silver, gold or even its eutectic alloys, that is what gives most of the problems. It is a transition metal that is much further away from metallic properties and closer to ceramics than, say, tin that is also a transition metal.
Surface tension plays a smaller role here because of the strange way it forms it's crystalline structure.
If OP wants to take advantage of it's straight edge crystals then I would put cold spots in the mold, drill some holes and put in copper wires to have just a bit of the tip extend into the mold giving bigger thermal gradient and have the solidification start at the cold spots, then try to time it right and pour out half the liquid metal.

You may be right as I do a lot of work with bismuth pewter, a tin/bismuth alloy, and not pure bismuth, but the surface tension does matter. Maybe not as much, but it will effect the surface finish.

Now while it may be closer to a ceramic in its properties than say, silver, but it does differ in a big way: water. When casting ceramics, a plaster mold will work great because the plaster will absorb the water, thus negating the issue of surface tension. Plaster will not absorb bismuth. The surface tension will effect the finish, regardless of the unique crystalline structure of the material.

Honestly if I were op, I'd cat into a high temp silicone mold because not only will it be better, but you can pull many copies from it. As for using talc, if you can find baby powder, that's the extent of the cost you'll incur to at least try to get a better cast.

*facepalm* didn't even think of that.

I've read everything so far and I'm trying to keep everything in mind, although I'm going to have to try one thing at a time. I won't be able to try again until Wednesday though probably, so I'll try to keep updating yall

Also if it helps yall, this is the original image that is more or less what I am trying to reproduce.

Also, is there any physical store franchise that carries vacuum grease? Amazon does not Prime any vacuum grease product and I don't want to wait for days.

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i dont know, we just have a bunch of tubes sitting around the lab since who knows when. maybe home depot?

Yeah, it looks like they do. I didn't do a proper search the first time. Also I named myself to avoid confusion.

also pencils have a lot of clay binders in them so it might be worth going to an art store and getting some art grade charcoal or something

Yeah, that occurred to me a few minutes ago. I live near one so I'll check it out.

i hope you succed bismuth robotnik

:D You got it

I remembered another question I had: If I get the perfect exterior egg , but it's bare inside, can I just fuse a pre-made bismuth crystal into the egg with a soldering iron? I don't have any trouble making independent crystals.

you know that's something i was wondering earlier looking at the picture of the commercial ones. i bet you couldn't really tell the difference without looking super closely

I'm just worried about getting something really fake-looking like this. (Not that this is the kind of egg shape I'm going for anyway.)

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Also, I finally understood what an earlier user said about a copper wire and a seed crystal! This may be exactly what I needed to keep crystals at the top from growing.

(When I tried making half-eggs out of an easter egg pan months ago, I could never get the crystals at the bottom to grow faster than the ones at the top surface.)

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>how to make it just form smooth.
Can't you just sand it down? I can't think of any moulding that doesn't need some touching up when you take the thing out of it.

Hardware stores have graphite powder for lubing locks and things.

It's hard to tell, but those holes are pretty deep. I would be sanding it down all day. I'd rather just do it smooth from the mold; I know it's possible from my experience with the Easter egg pan.

I'll probably end up sanding a little, though.

I'll look at that, but charcoal pencils will be my first try.

perhaps the soot from a candle will be enough? if you hold something in the flame it gets covered in soot very quickly

Absolute brainlet OP. Those are just pieces of bismuth shaved down and painted silver.

this

Fuck, I can see it now. I mean, I see the silver coating on the outside, I don't know how they shaved down bismuth to give it that egg shape It takes a lot of bismuth to make single pieces that big.

Had to look up "brainlet", haven't been on Veeky Forums for a while.

Anyway, I'll update with my latest failure, although I probably won't be trying the "make it with a two-sided mold" method anymore.

> Fucking brainlet can't tell what brainlet means

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So it volcanoed again. It also left that green residue where it (evidently) combusted.

I had drawn on the inside with an art charcoal stick, and none of that was present anymore when I removed the "egg". So of course I suspect that I did something wrong in getting art-grade charcoal, as someone is probably going to tell me.

Also, the egg dried nearly INSTANTLY again, even though I baked the plaster gradually up to 300 degrees. I barely had time to grab a metal rod to put down the hole before I came back to a solid egg.

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P.S. The second silver scrotum

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