Ok everyone: “Work-Hardening Fine Silver”.
Rio Grande has a Web page but no references to documentation.
https://www.riogrande.com/article?name=Comparing-Silver-Hardnesses-CGl
Can anyone provide any additional insights into this?
It has always been my experience that FINE silver does not work-harden.
Gerald,
Here is a book that talks about work hardening and annealing as well as a chapter on Silver and its alloys. I would quote you some excerpts, but I don’t have the book with me on holidays. It is in my teaching lab, but I seem to remember it talking about the topic you are wondering about. It is available from Otto Frei as well as at Amazon, or Brynmorgen Press. Hope this helps. Mike
Fine silver will harden and the grain boundaries are the issue- in a pure (relatively speaking versus common alloys) you will have a point of hardness that is the max for that metal. The issue lies in the grain boundaries and the effect of the crystals slipping along those lines. Annealing is the process of “reliving” the stress introduced by manual compression of those grain boundaries.
Shallow surface hardness can be achieved with a tumble with stainless steel shot which will burnish and compact the surface somewhat- but the core will still be relatively soft. (and the surface finish/details or texture may suffer due to the impacts of the shot)
To obtain a hard core to the item- hammering on a steel or hard block and then moving to final form with files, saw and hand tools will not remove the introduced compressive stresses.
Work hardening in your original question is relative. Fine Silver “will” work harden compared to an annealed piece of the same silver.
Your task is to identify what hardness you “need” to achieve for your end-use and then find the alloy that will match the use. I would look into the British coin formulas/alloys used over the years as theirs are well researched and written about and see why each was used, abandoned or adopted. Coins were soft in the “as struck” states and there was a need to make the coins last longer as well as show signs of tampering. (Although the tamper proof designs were not related to hardness- only fairness of commerce)
Hope this helps- not trying to be long winded. Nerd Alert- If you have a Engineering Library near you or a higher end academic library- Look into the ASM Handbook Vol 9 by George Vander Voort- it has a good section on alloys of precious metals- please dont buy this monstrous tome- its WAY too full of nonsense for jewelry work (unless you like to be the nerd and plan on doing casting/heat treating on an industrial scale)
I will ask at my library for this. It is one of the few books I don’t have!
My question was prompted by several part time and hobbyist jewelers who were posting about the right method to anneal fine silver.
I never have but my reply was dismissed as wrong due to info Rio Grande has on a web page.
I have been looking, and am not finding anything about work hardening fine silver. The most I can find for tumble hardening sterling suggests that the hardened surface is only in the neighborhood of 5 microns. So very thin at best.
I will look for the George Vander Voort book. There is a large engineering school at the University here so it should be in town. I will probably make a blog post about this in a few weeks when I have gathered more info.
Regarding the article in Rob’s link, there is information near the bottom of the comments, where Eddie Bell is answering a question, and it’s an analogy that makes crystal lattice distortion very easy to understand.
I’m not suggesting it to the knowledgeable participants of this thread, but many other Orchid members would benefit from reading it.
Yes. the information is good for STERLING silver. But I am trying to find information on the hardening of FINE silver.
This web page on Rio has me questioning where they got their information. I have already inquired about it and their documentation, they are checking for me. https://www.riogrande.com/article?name=Heat-Hardening-CGl
They list a Rockwell Hardness (Vickers?) of dead soft fine silver as 43, and of Spring hard fine silver as 80.
I have people telling me that you MUST anneal FINE silver as it work hardens (I have never annealed FINE silver). And I suspect that is true to a very minor amount. I am trying to find out what that amount of hardening is and why.
This web page is the only reference I can find to the various hardness of work hardened FINE silver.
I am just tracking down the documentation behind the slight amount of work hardening of FINE silver. I seem to have found a surprising rabbit hole.
That would be Vickers hardness. High carbon steel knives are usually hardened to Rockwell 55-60, which is roughly equivalent to Vickers 550-600.
Here’s a useful chart of hardness test number comparisons.
Hi Gerald,
Here is the work hardening chart for fine silver sheet that we have at Stuller. This is very old information and we have lost the source for it, sorry! The chart shows that fine silver can be definitely work hardened.
There is plenty of information about properties of “commercially pure” silver published in the Ninth Edition of Metals Handbook, volume 2, titled “Properties and Selection: Nonferrous Alloys and Pure Metals”. It is published by American Society for Metals (ASM) in 1979.
That book mentions the annealed hardness of very pure silver to be 25HV after annealing at 1200F.
Though the book does not show a work hardening chart (Vickers Hardness vs Cold Work (%)), it shows how the Tensile Strength varies with amount of cold work. In addition, it shows a chart for elongation in 2" gage length vs amount of cold work. That curve shows that elongation or ductility or fine silver flat lines at about 10% even when cold worked to 75%! Perhaps, this could be the reason why jewelers feel confident that there is no need to anneal fine silver?
Shan Aithal
Work hardening or fine silver.pdf (103.3 KB)
I will get a copy of the book. also, is it ok if I share this chart with information about where I got it from? Stuller. I would be using this info for a blog post of mine.
No problem, please share!