Ceramic crucibles

[Nobody Special]

Good evening,

My old casting furnace came up from Georgia with some stuff I had in storage, and my wife has gotten interested in green sand casting, so I bought her a couple of the old Gingery book series and I've been slowly assembling the bits and pieces for the sand, the flask, tools, etc. I still haven't replaced my crucibles, and although I'm sure that I will buy some proper, or at least cheap Chinese versions of proper crucibles, the last time I stopped I had begun experimenting with ceramics and had made a couple of plinths that held up well for several melts.

I'll probably get the Vince Gingery book on making your own crucibles, but I'm looking at recipes and the like online. I can get better fireclay eventually on the mainland, but right now what I've got is sodium bentonite, and there are the usual wild clays from the glacial leavings up here I can process easily enough. From most of what I've seen, more temper needs to be added than normal; rather than the 20% or so added to a wild clay to fire it in earthenware, it looks like a mix of more like 60 percent of silica sand or powdered grog with the remainder as fireclay for crucibles. I'm also curious as to whether you can add alumina to clay to improve its thermal survivability.

Preheating is of course crucial, anything homemade will be retired after a few pours if successful and I'll post any experiments on here, including the glorious failures from thermal shock and bad recipes. If anything, I'm planning precautions with the expectation of more failures initially than success. Heck, I've had failures from "good crucibles", and ask me how I first found out that molten aluminum gradually eats away the walls of heavy steel crucibles. (It involved my shoe soles going click click click everywhere I walked until I bought new ones). Any thoughts from someone more experienced in this?

Fair warning to anyone considering this, casting is inherently dangerous. I would recommend to any beginner to spend the money on good equipment and PPE, including premade crucibles. I also recommend they take classes or find a mentor with experience, and although I respect the people on iforgeiron, I would recommend not learning from most online sites or influencers. I got started in metal working by learning casting from online sites and I consider myself lucky to only have a few weird scars and to have gotten zinc fume poisoning once before I looked for better sources of information.

[Frosty]

I can NOT recall the name but we buy Zirconium flour from a supplier in Seattle and they carry almost anything ceramics or clay related. It was recommended as carrying clay suitable for making crucibles. Wish my memory worked tonight but I'm drawing a blank on a name.

Frosty The Lucky.

[Nobody Special]

I think they use it to make glazes opaque, so pottery places may have it, although I'm scared to look at the prices. I was mad enough about the sodium bentonite. I paid $60 for a 50-pound bag at a pottery joint in Tacoma when I went down to drill, and I used to get it as a pond liner at feed and seeds for maybe $6. Tried five places up here and only one even knew what it was. Nearest place that might have it or fireclay was two hours away in Everett. In the end, I paid without complaining, but it got me thinking about rigging a ball mill up again and it certainly has me looking at harvesting wild clays.

That's probably not economical either - in the end, it will cost me the time I could have used to make twice as much money and just buy what I want, but at some point, the whole fun of playing with metal is making something yourself from scratch. You just have to decide for yourself how far to take that.

[Frosty]

A 50lb sack of bentonite cost me less than $20 in Anchorage Ak. the same stuff, name and all costs about $25/lb at a pottery supply. Next time try a drilling supply, you might have to call a drilling company to find out where they buy drill mud but it's everywhere. I believe Parker Drilling has an office in Seattle area. They operate all over the Pac NW.

Frosty The Lucky.

[Nobody Special]

I'm a good bit north of that, but I can keep an eye out. Distance-wise it's not very far at all, maybe 55 miles, but with traffic on I-5 and the ferry, it can take two hours to get to Seattle, some days it's easily three or more.

If I make a ball mill, I can get all you can eat from crushed kitty litter, the cheap stuff. I've wanted one for a while, but ya know...make a tool to make a tool to make a tool...

Edited November 19, 2023 by Mod30
Excessive quoting

[Frosty]

No, I meant Parker Drilling as an example of someone you could call to find a closer source but that was probably a stretch. I'm used to being more than 2,000 miles from less common things. Drilling mud isn't one of those, there are a couple places besides pottery suppliers but both are more than 50 miles from me.

How much do you need? When I think of the cost of making a ball mill or driving 100+ miles round trip for a sack I start thinking of alternatives like just buying crucibles. 

I took a closer look at the map and it's one of those funny things, your place is more remote than ours though you're within driving distance of major population and industrial centers. I'd love to be within driving distance of the Boing surplus yard, I have a couple things I'd like to try but they need a jet or rocket engine alloy. And Federal Way, Whee DOGGIES!

I was born in Everett and have relatives all over the Pac NW. I have relatives who are almost neighbors of yours on Camano Island and another in Stanwood. Before we moved south following work when I was 5, I used to play with the Kickapoo neighbor kids and loved going to my Maternal Grandmother's place overlooking Puget sound, she had clear view of Hood and Hat islands from the Breakfast nook. 

Sorry for the side track but I love the PAC NW but I haven't lived there in 65 years, visited, oh yeah but haven't spent more than a couple weeks. It's funny how really early memories really stick, I can still smell the Everett aroma.

Frosty The Lucky.  

[Nobody Special]

So, went hunting today and found a couple of good clay banks and places with heavily clayed soils. Brought home four buckets, three of which were an almost clean greyish brown clay. I pulled out about a quart of the cleanest to play with and started on the rest - took about a half a bucket, mixed with water, and poured through a screen.

Tomorrow, I'll pour the water off leaving the clay underneath, then pour it into old pillowcases to let the water dry out. Mixed the stuff I brought in with sand for temper and made a mediocre coil and pinch bowl to fire to see how the clay behaves.

If it goes well, I'll set up molds to start making crucibles and playing with different ratios of ingredients and see what survives the furnace.

[George N. M.]

I once tried to fire clay spindle whorls in my propane forge using commercial clay I had bought at Hobby Lobby.  When I checked on them they had disintegrated and disappeared.  I had let them dry for a week or more prior to putting them in the forge.  I have no idea what went wrong.

[Frosty]

Did you "bisque" fire it George? A slow, low temp firing seems to be a must. I don't know much about firing pottery but I don't think I've heard of anybody firing straight from air or oven dried.

Best of luck Nobody, I'll be keeping an eye on your results.

Frosty The Lucky.

[Irondragon Forge ClayWorks]

Once clay is formed, it must be let stand until it dries to bisque prior to firing in a kiln. Or as Frosty said dried in a very slow heat until it's dry.

[wirerabbit]

If you are making crucibles, you need only fire the clay once, but the rate of temp increase must be slow during a few crucial temp. ranges. I'm not surprised that you did not have much luck firing Hobby Lobby clay in a forge, George. Too hot too fast or it was not a ceramic clay. The internet will supply you with the details. Many "clays" used in crafts are clay in name only or have fillers that can render them useless for our purposes.