HELP PLEASE : Platinum & Cobalt Custom Ring

[cmelb]

HELP PLEASE : Platinum & Cobalt Custom Ring

I''ve got a Master Custom ring made, I''m located in Melbourne Australia and I cant find anyone that caster''s Platinum without using 5% Cobalt.

And I have asked if they could use something other then 5% Cobalt and the answer is NO, as I have heard they can turn Blue and are Brittle is this true??

Any help appreciated.

 

[pricescope]

Some good information on different alloys here: Settings experts - alloys?

Garry (aka Precious Metals site)

 

[cmelb]

Hi Thank you for you fast response, I had a look and did a search on and I couldn''t find anything positive regarding Cobalt mixed with Platinum.

I called www.preciousmetals.com.au today and spoke to them who they get there Casting & settings by a company that uses 5% Cobalt in there Platinum.

I also had a read on these forums, that everyone that does casting in Melbourne uses 5% Cobalt in there Platinum.

Need to find someone in the next few days, or I will have no choice but to go with the 95% Platinum and 5% Cobalt.

 

[pricescope]

If I understood it correctly, Pt/Co alloy is hard (less prone to scratching) and better for Rhodium plating. It can develop a bluish oxide film especially if exposed to heat, which can be easily removed.

 

[cmelb]

If I understood it correctly, Pt/Co alloy is hard (less prone to scratching) and better for Rhodium plating.

What do you mean by Rhodium plating.

If I understand correctly are you saying that after they cast it with 95% PLT 5% Co do they need to Rhodium the surface..

 

[pricescope]

Platinum surface is mate. Rarely do people prefer the natural platinum color when given the choice - only a few super educated people. Rhodium plating is used to make it shiny. While it last, there is no risk for bluish oxide film. Rhodium plating can be repeated regularly - it is quick and easy procedure.

See also previous discussions:
Rhodium Plating
How long would or should rhodium plating last? Consumer experiences required
White Gold vs. Platinum for Satin Finish

 

[cmelb]

I will give him a call.

So basically if you use 95% Pt/ 5% Cobalt alloy you would need to apply Rhodium plating due to the Cobalt in the PLT to stop any bluish oxide film ?

 

[Jolly]

I looked into it too and I was told that all the casting companies in Melbourne use cobalt in their casting, but that in hand made jewellery casting doesn''t count. The usual alloy is copper and there are a number of other choices readily available. Cobalt is a casting alloy, not used in hand made jewellery. I was told it is a good alloy as far as successful casting is concerned - low porosity and it is a high quality metal in every respect (inc'' polishing and hard wearing). The draw back is the colour and the fact it oxidises. I then found that other casting companies in Australia are able to use much better alloys and it is just a matter of a phone call if anyone in Melbourne wants a high quality alloy. The best casting house (platinum alloy) is in Sydney, so there shouldn''t be a bother. At any rate, I had a piece made by hand and my jeweller made up his own alloy. As far as rhodium goes, I was told it does not bring extra shine where there is no polish but accentuates the dull spots. It is commonly used to brighten up the diamonds? And to hide gold solder joins.

On the down side, I was also told about many jewellers who lie and that most retailers care less about the alloy then people would imagine because 950 platinum, is 950 platinum. Apparently copper and cobalt are used because they are cheap and more expensive alloys are avoided.

 

[cmelb]

Hi Jolly, thanks for the info.

Would you name of the casting house in Sydney ? it might help some other Australians who are looking in getting the rings cast with better Alloys.