Question Cracking red gold
QUESTION: Hello,
I hope you can help me out.
Im a jeweller in New Zealand. I make Mokume Gane.
The problem Im having is that when I am rolling out a billet (6mm x 6mm x 30mm) the 18ct red gold is cracking severely. I am annealing to a semi bright colour and adding boric acid and meths for no firescale. I air cool the piece, and only roll it down 0.10mm each time, then anneal, air cool, roll...
But the 18ct red gold still cracks. The other metals in the billet are 18ct yellow gold and STG. They seem to be fine.
Please this is a very time consuming and expensive process, and I need to work this out!
I have added an image of the cracking for you too look at.
Any information would be great!
Thank you and cheers mate,
Izaak
ANSWER: Izaak, I always appreciate questions from jewelers. In some cases I am the one who learns and in all cases I do try to assist as I can. I see much work already with the billet in the photo.
Mokume Gane is a fascinating technique and with sufficient work may yield stunningly different and beautiful metal art in jewelry or other applications. Perhaps not understood by the non-jeweler is the tremendous labor involved in mokume gane, certainly if you prepare your own combinations of metals.
First, I am not an expert in this jewelry art form. My experience is some years old and limited even then. However, I do see one particular portion of your well described work method which is suspect.
Look at the annealing. You are using a slow cool from red and in most cases this would seem quite reasonable. However, almost any mix of red gold simply does not tolerate a slow cool very well. 18 kt (we use karat while you use carat and ct) red gold is most certainly going to have problems if heated red to anneal and then allowed to cool slowly. Cracking is almost a certainty when the metal is worked. I mentioned 18k since my experience with cracking is mostly with the 18k versions. I still would not slow cool lower karats of red gold.
What to do? Red gold is properly annealed as is some high karat white gold by quenching IMMEDIATELY when the red color is not seen in subdued light. Allowing the metal to cool below this temperature level invites and encourages cracking when the metal is cold worked such as with a rolling mill.
Although I cool silver generally a little longer or allow to air cool and the same is true of 18kt yellow, cooling these metals quickly to save the red gold should cause no harm. Suffice it to say, slow cooling is strictly a high risk with red gold and if this is ruining the billet, then you must put the other metals in the billet to the same treatment simply to save the red.
Izaak, I am working from a somewhat generalized chair, where I am sitting now. I have not seen the billet produced and do not know the particular alloy of red gold you are using. From this limited view, red is red is red and the annealing cooling process should be changed. At least try it! I am not sure if anything can be done to salvage the exposed piece of gold on the top of the billet in the photo. This photo shows typical cracking to be expected under the conditions. Izaak, I do thank you for the fine photo. As a jeweler, imagine trying to explain some aspects of the work and metals with words only! When allexperts.com finally gave us image capability my world of answers was blessed tremendously.
I certainly hope my recommendation will solve the problem. I cannot guarantee results but cannot argue with the truth of red gold and the need to quickly quench from red heat.
God Bless and Peace. Thomas.
---------- FOLLOW-UP ----------
18ct yellow gold, 18ct
QUESTION: Dear Thomas,
Thank you very much for responding so quickly. I have used your advice and have been able to complete my job.
Also I spoke to the refinery whom I purchased the 18ct red gold off and here is what he had to say:
"18Red is a very difficult alloy to use. Not only is it hard and work-hardens quickly, it also develops a large grain structure. It needs to be worked hard and annealed at cherry red and then quenched so as to stop the formation of excessively large grains that crack at the grain boundaries. Good luck!!!"
I have attached an image of the finished piece.
Once again many thanks and god bless,
Izaak.
AnswerFollow up--------------------------------------Last from Thomas---------------------------------
Izaak, the photo is showing a wonderful ring with beautiful pattern. I am certainly pleased I was able to help you complete this difficult project. To know you have done well with a difficult metal is something I wanted to hear. Thanks for asking in the first place and I am again glad I was able to assist. Best to you in the future. God Bless. Thomas.
-------------Original question---------------------------------------------
QUESTION: Hello,
I hope you can help me out.
Im a jeweller in New Zealand. I make Mokume Gane.
The problem Im having is that when I am rolling out a billet (6mm x 6mm x 30mm) the 18ct red gold is cracking severely. I am annealing to a semi bright colour and adding boric acid and meths for no firescale. I air cool the piece, and only roll it down 0.10mm each time, then anneal, air cool, roll...
But the 18ct red gold still cracks. The other metals in the billet are 18ct yellow gold and STG. They seem to be fine.
Please this is a very time consuming and expensive process, and I need to work this out!
I have added an image of the cracking for you too look at.
Any information would be great!
Thank you and cheers mate,
Izaak
image: Jewelry-Gems-Minerals-689/2009/10/Cracking-red-gold.jpg
ANSWER: Izaak, I always appreciate questions from jewelers. In some cases I am the one who learns and in all cases I do try to assist as I can. I see much work already with the billet in the photo.
Mokume Gane is a fascinating technique and with sufficient work may yield stunningly different and beautiful metal art in jewelry or other applications. Perhaps not understood by the non-jeweler is the tremendous labor involved in mokume gane, certainly if you prepare your own combinations of metals.
First, I am not an expert in this jewelry art form. My experience is some years old and limited even then. However, I do see one particular portion of your well described work method which is suspect.
Look at the annealing. You are using a slow cool from red and in most cases this would seem quite reasonable. However, almost any mix of red gold simply does not tolerate a slow cool very well. 18 kt (we use karat while you use carat and ct) red gold is most certainly going to have problems if heated red to anneal and then allowed to cool slowly. Cracking is almost a certainty when the metal is worked. I mentioned 18k since my experience with cracking is mostly with the 18k versions. I still would not slow cool lower karats of red gold.
What to do? Red gold is properly annealed as is some high karat white gold by quenching IMMEDIATELY when the red color is not seen in subdued light. Allowing the metal to cool below this temperature level invites and encourages cracking when the metal is cold worked such as with a rolling mill.
Although I cool silver generally a little longer or allow to air cool and the same is true of 18kt yellow, cooling these metals quickly to save the red gold should cause no harm. Suffice it to say, slow cooling is strictly a high risk with red gold and if this is ruining the billet, then you must put the other metals in the billet to the same treatment simply to save the red.
Izaak, I am working from a somewhat generalized chair, where I am sitting now. I have not seen the billet produced and do not know the particular alloy of red gold you are using. From this limited view, red is red is red and the annealing cooling process should be changed. At least try it! I am not sure if anything can be done to salvage the exposed piece of gold on the top of the billet in the photo. This photo shows typical cracking to be expected under the conditions. Izaak, I do thank you for the fine photo. As a jeweler, imagine trying to explain some aspects of the work and metals with words only! When allexperts.com finally gave us image capability my world of answers was blessed tremendously.
I certainly hope my recommendation will solve the problem. I cannot guarantee results but cannot argue with the truth of red gold and the need to quickly quench from red heat.
God Bless and Peace. Thomas.
---------- FOLLOW-UP ----------
QUESTION: Dear Thomas,
Thank you very much for responding so quickly. I have used your advice and have been able to complete my job.
Also I spoke to the refinery whom I purchased the 18ct red gold off and here is what he had to say:
"18Red is a very difficult alloy to use. Not only is it hard and work-hardens quickly, it also develops a large grain structure. It needs to be worked hard and annealed at cherry red and then quenched so as to stop the formation of excessively large grains that crack at the grain boundaries. Good luck!!!"
I have attached an image of the finished piece.
Once again many thanks and god bless,
Izaak.
