Crucible / melting dish types

[Militoy]

Hope this subject hasn't been covered ad-nausium. I have gone through several searches on melting dish and crucible types, and I'm still not clear on when and why to choose a particular type. I just busted one of my last clay dishes - and I'm looking for a little more guidance on the differences between graphite, silica, fire clay etc. crucibles, and the different shapes available. Unfortunately - pretty soon the only ones I may have available are the historic ones from my 'ghost town' gold mine. I'd love to fill those up - but they're 2-3 feet tall! I'll probably go with a few of Steve's offerings - but I would like to get a better idea of the differences between the types before I order. Thanks for any insight from the experts!

EDIT - BTW - I also have a pretty good collection of iron dishes, ladles, spoons and crucibles that were in the blacksmith shop when I bought this place. Most of the ingots we found were babbit - and I'm guessing that's what they were mostly used for. I'm curious whether PMs would ever have been melted in iron crucibles?

 

[Harold_V]

Thanks for any insight from the experts!

I'm not convinced I'd call myself an expert, but my routine was to use the small shallow melting dishes that are commonly used in the jewelry industry. I believe they are the same units offered by lazersteve. They are inexpensive, and will hold up to multiple heats and can be cleaned (chemically) to restore them to useful service when they have been heavily coated with dirty flux. I'm assuming you do your melting by torch, not by furnace, and that you have modest quantities to melt, something less than 20 ounces.

For clarity, I used just such dishes, albeit the largest ones made, to do all of my melting, including melting large volumes of twice refined gold. They were, for me, a perfect fit.

EDIT - BTW - I also have a pretty good collection of iron dishes, ladles, spoons and crucibles that were in the blacksmith shop when I bought this place. Most of the ingots we found were babbit - and I'm guessing that's what they were mostly used for. I'm curious whether PMs would ever have been melted in iron crucibles?

Absolutely not! Not under any circumstance, and that includes having applied a refractory wash to the items.

Reason?

Molten metals are very strong solvents of other metals. They will readily dissolve some of the iron, which is then absorbed by the molten values. Further, if your item happens to be cast iron, its melting temperature is well below the melting point of the platinum elements, although I expect that's not what you had in mind.

Never melt values in metallic vessels of any kind. If they don't dissolve the vessel, they most likely will solder to the vessel. In any case, it's nothing but trouble. Always use proper melting vessels. You can't really afford not to.

Harold

 

[dtectr]

Can you still buy the 2-piece melting dishes that were used in centrifugal casting machines by the smaller sized jewelers? They form kind of a furnace effect with the top attached. They also held the heat longer, so the material would still be molten when flung at the mold by the spring loaded arm.

I was wondering if they would work for some of the sizes of melts we do? :idea:

 

[Militoy]

...I'm assuming you do your melting by torch, not by furnace, and that you have modest quantities to melt, something less than 20 ounces...

....Molten metals are very strong solvents of other metals. They will readily dissolve some of the iron, which is then absorbed by the molten values. Further, if your item happens to be cast iron, its melting temperature is well below the melting point of the platinum elements, although I expect that's not what you had in mind.

Never melt values in metallic vessels of any kind. If they don't dissolve the vessel, they most likely will solder to the vessel. In any case, it's nothing but trouble. Always use proper melting vessels. You can't really afford not to.

Harold

Thanks for your reply. Correct on all your assumptions: I'm using a torch; melting non-platinum PMs only; and my batches are well under 20 ounces each. I do have a propane-fired forge I could rig up as a furnace - but there's really no need to with the small size of my melts. I'm limiting my largest "ingot" size to one ounce, and not planning on selling any, at least for the present.

The thought of losing gold to a metal crucible by soldering crossed my mind; but I didn't even consider the idea of poisoning the gold with iron. I'll leave the iron ones in the blacksmith shop for casting bearings, bullets and sinkers.

So I suppose I should stick to the shallow dish type for now. I don't have any with the pour 'spout' at present so I guess I don't particularly need that feature. I'm still interested in the difference between the silica and fire clay dishes. Maybe better thermal shock resistance from the high-$ ones?

 

[Harold_V]

I'm still interested in the difference between the silica and fire clay dishes. Maybe better thermal shock resistance from the high-$ ones?

I, more or less, avoided voicing my opinion, not being well versed on the silica dishes. I have used them, however.
They most likely are somewhat more stable, and certainly heavier in cross section, so they are likely to enjoy a much greater lifespan. I think the chief reason I avoided them was because of the limited volume, although large sizes may be available. Bottom line, at least for me, was that the clay dishes (only the white ones, never the tan ones) served my needs perfectly well, and were easy to handle and readily available locally, when I refined. That is no longer the case. Freshman's, in Utah, no longer carries the large dishes, for reasons I do not know.

Harold

 

[nickvc]

Harold perhaps their major customer closed shop and retired!

 

[Harold_V]

Harold perhaps their major customer closed shop and retired!

Heh! Could be! If memory serves, they still sell the smaller sizes---it's just the large one that was no longer available. That was about a year ago, however. Who knows what they offer today?

Incidentally, they are the major supply house in Salt Lake City for the jewelry industry---although they do have competition.

Harold

 

[samuel-a]

Militoy

I don't know how relevant it is exactly for you, but i think you will find this document quite interesting:

Matching Your Crucible to Your Application

You can find it and download it in the books and guides page on my website.

Edit: here is the link

 

[butcher]

A free download of HOKE'S book, nice samuel-a.

 

[skeeter629]

I get my dishes from Contenti. I have used them for a few years now, and am rather happy with them. I order the Open Melting Crucibles - 3 1/2 inch works great for me. I called them about 6 months ago and we worked out a deal if I bought 50 at a time. They gave me a discount on them.

 

[samuel-a]

A free download of HOKE'S book, nice samuel-a.

Sure, the more sources for this book the better...

 

[butcher]

Even better You have a hard back copy for a very reasonable price, wish I new that before I bought mine, well someone else may need one.

 

[samuel-a]

Even better You have a hard back copy for a very reasonable price, wish I new that before I bought mine, well someone else may need one

Yes, thanks to GoldSilverPro.
First, i only found hard copies for sale on ebay/amazon at outrageous prices.
I took them off and replaced them with GSP's links to hard copies at much reasonable price, but i think i'll add the amazon links back, in case the other source runs out or no longer available.