Help with Casting Platinum

[samatheang]

Does anyone have this problem with casting Platinum or know why it is like this? I am using Emerald resin and Invest RP with Centrifuge. I am sure it has nothing to do with the resin or the curing because I am casting fine with gold. It always comes out with rough surface and very fragile (Break when bent). Any idea would be much appreciated. Thank you.

[ELYPSI]

Did you reused the platinum from another casting?
How many times are you using the same crucible for casting platinum?

[samatheang]

Did you reused the platinum from another casting?
How many times are you using the same crucible for casting platinum?

Thank you for your response, Elypsi.

Yes, I reused the platinum from another casting, and I have been using the same crucible for about ten times already. Do you think those are the problem?

How many time do you think I can reuse the platinum? Same thing for the crucible, how many time before I replace it?

Someone told me that maybe because I didn't use enough platinum. Since the extra platinum at the bottom of my tree is too little, there is not enough force to push the platinum in while casting. I don't think that's the problem. What do you think?

Thanks again for the help.

[nillard]

I only use my centrifuges machine when casting platinum... Also use different investment.. Have you had success with platinum before?

[ELYPSI]

I have an indutherm and they recomend to use the crucible maximum of 5 times.
With gold castings I reuse part of the metal from other castings, but platinum is more tricky, so we always cast with new platinum.

[samatheang]

I only use my centrifuges machine when casting platinum... Also use different investment.. Have you had success with platinum before?

I haven't had any success yet. It always come out with rough surface like the picture. I have tried both regular R&R Platinum Investment (Not the Plasticast Plat.) and Invest RP. I heard a lot of good thing about Invest RP, and I got better result than the R&R too. Just not good enough.

[samatheang]

I have an indutherm and they recomend to use the crucible maximum of 5 times.
With gold castings I reuse part of the metal from other castings, but platinum is more tricky, so we always cast with new platinum.

Thank you, Elypsi. I will try it with new platinum and new crucible. By the way, do you use pure platinum or 950? If 950, what do you mix your platinum with? Thanks.

[ELYPSI]

Platinum 950. Investment R&R

[samatheang]

Platinum 950. Investment R&R

I meant do you mix pure platinum with alloy to get 950 or you just bought the 950 Platinum? If you mix it yourself, could you tell me what kind of Alloy do you use please? Thanks.

[jefree]

the breaking apart problem has to do with not enough heat, the casting must fuse, what you have is like sand pressed together, it fine until you bend it etc... that's why it is matted instead of shiny. When you cast platinum, keep heating until it has a white glow around it, that's the only way I remember.

Most investments today produce a rather rough casting in platinum, if you really know what you're doing (I don't know enough) you can obtain a smooth casting . After 40 years of casting I now use Zero Porosity who have the capability to produce smooth castings in platinum, they are probably the best casters available to jewelers.