Melting points for various types of metal

[Autumn]

Hi,

I'm in the early stages of a project and haven't decided on the metal type yet. I am also completely un-experianced.

What are the metlting points of various types of alloys used for jewellery?
I'm thinking silver, gold, platinum and palladium alloys.

How achivable are those melting-points with a home-kiln?
Could I realisticaly melt palladium? Or am I bound to only using gold and silver alloys?

Many thanks,
Autumn

[Dennis]

This is quite a tall order, as the melting range of the various silver alloys, gold carats and solders are all different.

You could decide on likely alloys and look them up on line. Some melting ranges are given here on Cooksons website: http://www.cooksongold.com/category_...ange+of+alloys

They are also available in tabulated form in their printed catalogue. Dennis.

[josef1]

do you want to cast the metal or solder it ?

[enigma]

A reasonably priced small kiln will generally have a top heat of around 1100 degrees C which will allow you to do silver, 9ct and 18ct yellow and rose gold but not white. Definitely not Palladium or Platinum which have a very high casting point.
Mine cost around £600 new from Palmer metals and is great.
I have another one which goes to 1300 degrees C which should do white but haven't actually tried it yet- any tips on casting white Josef? I know that I had to hold yellow at full temp for a long time to get a liquid enough pour .
You also need to remember that casting point is generally higher than melting point.
I think most people just send off their casting actually as the full set up for lost wax casting is pretty expensive- I use Delft clay.

[Icarleug]

By no means a caster or metallurgist, but I did research it myself (since I want to be able to make my own alloys some day).

If you want to cast palladium (as in the 95% pure stuff) you really need a controlled atmosphere and high temperatures, so I doubt that any hobby kilns would suffice.
Palladium absorbs oxygen when melted and then expels the oxygen when solidifying, so if you don't have a controlled atmosphere it will cause porosity due to trapped oxygen in the metal structure.

For the melting point of alloys (assuming you buy them and not alloy them yourself) you should look it up at the supplier, since they probably have their own blend of metals.
Attempting to alloy it yourself you will probably need a recipe and a phase diagram that tells you the melting temperatures of pure metal plus the melting point of the alloy so you can adjust accordingly when casting it.

Here is a quite useful chart for pure metals: http://www.kitco.com/jewelry/meltingpoints.html
Lots and lots and lots of metallurgy info and phase diagrams for 18 carat gold: http://infoscience.epfl.ch/record/14...PFL_TH4635.pdf

/Andreas

[ps_bond]

My kiln will also get to 1300C, but it was purchased for heat treating steel and some of the alloys can be a bit obnoxious in their temperature requirements. You can retrofit an inert gas purge to a kiln, but it is very wasteful of gas as standard kilns aren't designed to be gas-tight, so you have to run a constant flow.

[enigma]

What do you mean by 'obnoxious' Peter? is there a chart anywhere that gives average times they need to be held at temperature? I tend to leave yellow for about 45 minutes to an hour ( at 1100) as I found if I pour earlier it goes too thick/viscous but that does seem like a long time?

[ps_bond]

Obnoxious running up to 1300C and having multiple stages of HT, for example. Funnily enough, there are Time/Temperature/Transition diagrams for metals (TTT) for heat treating; the HT directions usually detail schedules according to section thickness (i.e. soak 30mins per cm @ x temperature). All the casting I've done has been torch-fired rather than kiln, which is much faster than that - sounds a long time, but I know the heat transfer isn't great.

[enigma]

Thanks Peter, probably gets quite complicated then by the sound of it!
I can melt it pretty quickly but just found that its too viscous to pour if I try earlier even after adding some borax- assume its still borax for gold?
I only have a Sievert on propane so no good at casting
Still I like the kiln, its less hassle and doesn't involve scaring myself to death with a great big flame

[ps_bond]

I only have a Sievert on propane so no good at casting

Really? News to me... Depends which tip you use though; I have one of the roofers tips which is overkill for most things, including casting small amounts of silver & gold. Most of the time I use the 3941 with some firebricks to keep the heat in/shield the surrounding area.