Molds

Looks like I'm going to have to try sand casting these. The plaster outgasses something terrible when the hot bismuth is added disturbing crystal formation. My first couple of attempts all ended with a very thick rough inner surface and maybe the edge of a crystal.
I have also spent a whopping 4.50 on a box of borax to use for flux. I think this might cut down on the grey scum oxide layers formation.


Olivine sand and bentonite clay....

Busy Busy

I have managed to destroy 1/2 dozen eggs, and made quite a mess. But I now have 2 molds. A very basic half round, and a 2 piece full egg. I made the molds out of plaster of paris which burns at 1200F since the bismuth will be poured around 700, they should hold up for awhile. I will use the half round to test things. I suspect I need to preheat the molds for best crystal growth. Slower cooling = larger crystals. I was worried about a good mold release, ideally carbon based. I remembered a solution and just sooted the mold with a lighter. We will see how well that works.
I'm going to the supply store to pick up some safety equipment Monday, I don't feel like getting burned.
Later in the week I will start melting (fingers crossed) and growing crystals.

Modeling clay and a wax cast egg.

 I embedded the wax model egg halfway into a slice of modeling clay and built up a back from there that fit nicely when wedged into a stainless steel bowl.

Wax egg and a poured plaster half.

 I wedged the clay face in the bowl and added some supports. I needed more supports plaster is heavy when wet.

Finished mold with the opening to pour the excess out of.

Once I had 1 half the other half was simple.

Simple simple

I poured some plaster and stuck one of my wax eggs into it.

Well I have the bismuth sitting here, and have been working on egg molds. I've been trying to do it in a half-assed manner and surprise surprise, I've learned several important lessons in what not to do.

Getting the positive image of the egg in paraffin has proven easy. Well easy since I'm not after a whole egg my vision is a little different. I'm not positive if cutting the top off or cutting an angel off will work better so I'm trying both. 

Getting the halfway mark on the egg has proven a little more challenging

I'm going to have to break down and get some modeling clay, and possibly some RTV. In the meantime I'm waiting for the IR thermometer to arrive.

The bismuth arrived from rotometals a day earlier than they promised. If its fudged math or just great shipping either way it left a smile on my face.

2 pounds is smaller than I expected. It actually weighed 2 grams less than a full 2 pounds

A quarter in the foreground for reference.
I think I will need to make needles with some of this for suspended crystal growing, or I need to make an egg mold. Decisions decisions, but soap first. I plan to start playing with hot metal in the beginning of march.

2 pounds of bismuth 99.99% have been ordered and should arrive by Friday!
Looking through my old equipment I find I still have an unused hotplate and ladle for pewter casting. WHile I wont be able to play in the controlled environment I wanted too, I have enough materials and tools to get started, and produce a few pieces of my own to take photos of.

I have about 120 pounds of soap to make this weekend, I will start playing with bismuth when I am done with that.

Work space

The basic project can be done on a stove top but for control purposes
I want
a glove box/flow hood, Commercial glove boxes seem to start at about 1000$

a scientific hotplate for exact temp control

an induction hotplate for rapid melting
an IR thermometer
a flow regulator and lines for the shield gas
a bottle of argon
a couple graphite crucibles
a refractory board to protect the plastic in case of spills
Kaowool to insulate the crucible to slowing cooling for crystal growth testing
gloves that attach permanently to the box and create part of the seal
some oven mitts (the industrial kind)

I could probably get away with, several less exact options for this testing but I would hate to figure out I needed a proper glove box 3 weeks into the project.

My design so far is a box with a slanted front for viewing. Currently I'm aiming for 24L X 20W X 18-30H
18 inches at the front 30 in the back.
I'm planning on the following
Black ABS for the sides, base and back. I would prefer white for thermal reflectivity, but the thicknesses I want seem scarcer and therefore more expensive. ABS has good thermal properties which are a concern for this project.
The front, and top will be clear Polycarbonate. This plastic is fairly stable thermally and will put up with the mechanical wear, and stresses of the glove holes very well.
At tap plastics the pre cut pieces would run me just around 220$ for materials and another 40$ or so in labor to laser cut the parts to proper shape.
The box also needs gloves. These are usually attached inside and outside of the box with a pair of circular gaskets.

It would look something like this...

I will need power and a gas connector, valve on the exit. 

Last bit is the tricky bit of opening and closing the box while still being able to seal the box. 

Oxidation control and purity concerns

In my research I saw the importance of oxidation control, this will keep the expensive purity you paid for. This can still be done in open air, it just cuts down the number of times you can remelt bismuth and still get really nice oxidation colors on the crystals. What you melt the bismuth in is also important. Liquid bismuth will alloy with most metals in very small percentages, but even small adds up when your starting at 99.99%. Stainless steel works, but if you plan on remelting several times and still want good results you want a graphite crucible like the kind used in gold and silver casting.

Controlling the air in your crucible isn't actually too hard. A lid during heating will certainly slow down the skin formation. I plan on building a simple flow hood, not for the skin formation, but so I can attempt to determine the critical oxidation temps/rates. Since bismuth naturally oxidizes in air, there isn't going to be a hard temperature at which the colors form. It will probably be a time/temp/mass graph.

For this project I want precise temperature control which will require a scientific hot plate. Luckily a hot plate still works in a non oxygen atmosphere.  A basic flow hood really isn't more than a box with a door and a bottle of shield gas, But I figure I will spend the 50% extra time to do it much closer to right. there will be pictures later, hopefully I get funded.

On a side note it appears you can reclaim that bismuth oxide scum by heating   it to a high temp with carbon under a shield gas. This probably wont be useful unless you are manufacturing things with bismuth, and going through many melt cycles.