EFFECT OF BLUING PROCESSES ON INLAY METALS

[AllenClapp]

I recently saw a question on an engraver forum concerning 24kt gold being turned to a rose color by a nitride process. I became concerned about a multi-metal inlay project I was planning and I corresponded with Turnbull Restoration, LLC to inquire about bluing processes that did or did not affect various inlay metals. Specifically, I asked about 24kt gold, 14kt rose gold, fine silver, titanium, copper, and brass. (NOTE: the Turnbull website lists processes used by them.)

In the first response from Sara Turnbull, she said the following.

I passed your questions along to our quoter, who didn't have much time to respond but was able to tell me this:
"The only inlay that I am aware of that we have blued are white, yellow & rose gold. They are inert to Carbona & hot blue. I think they are inert to rust blue but I don't know for certain."

Sara followed up with the following and gave permission for me to post this info on engraving forums.

I happened to have Steve Lester and Doug Turnbull in the room with me when I came across your email again. Here's what they could tell me:
“All of those metals can be blued or color case hardened. Copper will tarnish with use and time, but it won't be harmed by the bluing processes. With hot bluing the inlaid metals often require less clean up after bluing, whereas the super high temperatures of charcoal bluing and color case hardening may release impurities in the precious metals and require some attention afterwards. As for 24kt gold being turned to rose gold via a nitride process, we can't speak to that as we don't do anything with nitride finishes.”

 

[JJ Roberts]

Al copper inlays will kill hot bluing the salts will be no good and will have to be replaced rust blue OK. J.J.

 

[707chrisa]

I don't Know if this helps but there is an old formula that had a gold "salt" in it for red glass. Some say this story of gold in red glass was just a ploy to make it seem to cost more than it did . AuCl3 is a red orange common compound of gold and chlorine . I don't know if this is your culprit, but in the dental lad I worked at I cast a lot of gold some of the alloys had some wiled as cast colors. We would sand blast off these "oxides"( gold dose not form any true oxides at room temp) bead blast and then heat to a red heat in a vacuum . Long story short if you had to you could remove the surface discoloration with polish, this would be a pain in the butt on a blued gun. Most of my work was with 16 to 18 kt but 24kt can discolor too.
The bead blast was to help close any surface pores or micro voids just under the surface then steam clean . We used one bure for each alloy carbide only. This would be over kill , but the point is wire inlay is asking for iron contamination.

 

[zzcutter]

To follow up with the question I asked.
I recently did a K32 that I did 24kt gold inlay work and also 18kt green gold inlay work.
It was returned to krieghoff germany to have them do there nitride finishing process and when returned the yellow gold was all rose colored but the green gold was fine.
I and KI tried to resolve the issue in many ways but nothing worked. When i cut the detail in the gold you could see the yellow appear in the cuts. So I deducted that the process somehow plated copper to the yellow gold or bonded to it but didn't to the green gold. But I am really guessing and don't know.

All this work went through Krieghoff International so no fly by night here. In the end the client was still happy as it was His and KI decision to return it to Germany for that finish.

So just was asking for the reasons stated above so if anyone would know of a cause please let me know your thoughts.

thanks Jon

 

[Goldjockey]

Plating effect is an interesting idea. It's why jewelers use copper tongs rather than steel to take items out of hot pickling solution. What happens within the (acid based) pickle is that over time, copper which is present in sterling and other alloys leaches out and is suspended within the solution. When steel or iron is immersed in the solution a chemical reaction occurs and copper will plate directly onto the surface of the steel.

 

[Si si]

Plating effect is an interesting idea. It's why jewelers use copper tongs rather than steel to take items out of hot pickling solution. What happens within the (acid based) pickle is that over time, copper which is present in sterling and other alloys leaches out and is suspended within the solution. When steel or iron is immersed in the solution a chemical reaction occurs and copper will plate directly onto the surface of the steel.

After taking classes with Wes Griffins I learned from him of using a toilet bowl cleaner for pickling that prevents those issues with the traditional pickling, and no longer have to worry nor use just copper tongs as I once needed to. He can explain it better than I but I thought I would just added to your comment as a said note for it’s kinda interesting. Cheers