x-ray test

[amena]

I did get tested by x-ray a small tray that has a flat bottom and the edge worked in repoussé. It is made in one piece without any welding.
They did a series of measures on the plate bottom, and found rather different results. The average of the measurements made on the bottom is about 870/1000, the same way they did a series of measures on repoussé edge and the average is about 910/1000.
I was not allowed to attend in person at the test, so I can not but take note of the results.
Someone who has more experience than me can explain how different results are possible on the same plate?
Amena

[oel]

Pure silver is hardened and made into an alloy of silver with copper, sterling standard (92.5% pure silver mixed/hardened with 7.5% copper), other standards could vary between 80% pure silver with 20% copper. Sometimes the silver alloy is not a homogeneous mixture and on a sheet of silver the overall minimum silver standard could vary a little; this could be due to the art of making a good silver alloy; the blending/fusing process of mixing copper with pure silver. Silversmiths do not shape the metal while it is red-hot, but instead, work it at room temperature with gentle and carefully placed hammer blows. The essence of silversmithing is to take a flat piece of metal and to transform it into a useful object using different hammers, stakes and other simple tools. It has been explained to me that the hammering and working of a silver (alloy) sheet could force a little copper in the silver alloy to a different direction, thus creating little clusters in the silver alloy with less or more copper ‘attached’ to the amount of pure silver.
In your case the overall minimum fineness of the silver is .870 and today a Dutch assay office should mark your plate ZII minimum fineness of .835

Oel.

[Francais]

It might be interesting to see the piece, and judge where it was made. Modern silver alloy is more standard than antique, and as Oel says some silver alloys can be inconsistent across a piece. The worst I have seen was a large Mexican tray which had several places where the increased copper content was noticeable. There is a simpler explanation for the edge being of higher grade silver. When a piece of silver is worked, it becomes brittle and has to be annealed. Part of the annealing process with anything besides pure silver, is to dip it in acid, after it has been heated to the necessary temperature, to remove the tarnish caused by the heating process. The acid removes copper, but not silver. So after dipping the surface is purer silver. Of course there would be no difference between bottom and edge if the whole piece was heated and dipped. But in your case it seems likely that just the edge was heated and dipped. You don't mention whether the bottom and top of the middle assayed the same. Several books on American silver show the results of testing various pieces of silver and the variations found across the various parts, or places on the same part. I hope this explanation isn't too poorly phrased. I would be happy to recommend a few of those books, if you are likely to find them in your location.
I would also point out that what Oel suggests is absolutely correct. Most countries had certain MINIMUM standards, but there was nothing, except expense, to preclude the silversmith from using a higher standard for the piece.

Maurice

[Hose_dk]

In the old times a "oldermandsranke" was used for testing. The method was to take pieces of silver from an object. I this case the beaker is around 3 cm across. A lot of surface was tested on this small beaker anno 1800. To make sure that on avarage the contenth was as requiered.

[amena]

Hi all
Your remarks make me more clear the matter.
The piece in question is the small tray which is discussed in my topic "Hard task" and is quite old.
Admin edit the images.


The final outcome of the analysis on the flat part says:
In examining the bottom, it shows an average quantity of copper around
130/1000 facing an average of silver 870/1000.
This is quite in line with expectations, as the fineness of Malta was 10.5 / 12, i.e. 875/1000.
However, values ​​were found from 800/1000 to 882/1000, with a deviation of more than 10%.
If I understood correctly the question, Maurice asks if the test was done on both sides of the flat part. To this question I can not answer with certainty, because, as I said, I could not attend the test, but I think it was made only on the bottom.
I would be very interested to know the titles of those books that describe the variations found during the test, although I think it will be very difficult to find in Italy.
Thank you all for your help
Amena

[Joerg]

Dear all
In German language we say „Wer misst, misst Mist“. In English, “all measurements are erroneous”. Generally, in a measurement you can have two types of errors: Errors in the sample, for example the point of measurement is not representative for the whole object and errors in the measuring chain, for example inaccuracy of the measuring device.
In the current responses we discuss the first group. Errors in the sample. I would like to point also at the second group of errors, in the measuring chain.

I assume you had done an analysis with x-ray absorption spectroscopy. Here some Wikipedia articles to this measuring method:
http://en.wikipedia.org/wiki/Absorption_spectroscopy
http://en.wikipedia.org/wiki/X-ray_abso ... ectroscopy
I must say, in this respect the German article is more comprehensive:
http://de.wikipedia.org/wiki/R%C3%B6ntg ... enzanalyse

Generally spoken, you should not take the results for granted, there are measuring errors. Such measuring devices are rather expensive. Hand-held versions starting at 10’000$ while more accurate stationary devices can easily cost much more. So, the accuracy is also question of the quality of the instrument. Also calibration is essential, if the device is calibrated for silver or for another use. Then if the sample provides surfaces which are optimized for measuring or not. I was last year testing some silver spoons. The measuring device needed clean, fine (polished), flat surface. Of course my spoons could not. So the result was more inaccurate than with a flat, polished piece. Also the result depends strong on the measurement duration. A duration of more than a minute is recommended. I do not know if your sample was measured that long.
You should ask the people doing the analysis for details. Type of analysis, accuracy, calibration status etc.
You mentioned a lot of measurements were taken with a wide variety of results. This points to problems in the measuring chain, less than in the sample.
To not take accuracy on electronic, sophisticated devices for granted.

Merry Christmas

Jörg

[Francais]

Thinking it over, and seeing the piece, I think Joerg is right. It doesn't appear to me to be repoussee work, but flat chasing. If this is the case the edge was probably only slightly more worked than the bottom, as flat chasing does not require annealing, or at least not as often. Also if they tested the top edge, they didn't have a flat polished surface on the edge. Finally they probably used a hand held machine, as the piece was probably to big for a stationary one. The person who tests for me works at a large smelt, and says they can't test anything larger than about 6 inches, and on a piece that size, only in certain places. So it ended up to be quite accurate on the "Papal Spoon", but to test a large piece they would have to melt it into a bar.
The end result is there are too many variables. So ultimately there probably isn't an answer to the query, except to say that many, many things could have contributed to the results.
Nice piece though.
Also it was interesting to see the Hose_Dk's piece, seeing the assay cuts, and so many of them, on a French piece is very unusual. It is probably worth a discussion on its own.
Maurice

[amena]

Joerg is surely right. It reminded me of what my professor said, many (too many) years ago.
However, with regard to the edge, I believe that the first observation of Maurice about annealing and the acid treatment is right.

The decorative part in the red perimeter is actually made by flat chasing, but the embossed edges marked by the green arrows, are made in repoussé.
In any case, this discussion has been very informative for me, and hopefully for others.
I thank all the participants for their comments.
Best wishes
Amena

[Francais]

This is nit picking, but I don't agree with your definition of repoussee. Quite honestly I enjoy getting off the subject sometimes, it forces people to read threads, which otherwise wouldn't interest them. Repoussee refers to a decorative technique achieved by pushing the metal in one direction then pushing it back the other way from the other side. So the inside or other side of the decoration is a mirror image of what shows. I think if you look on the back of this edge, you will not find a reverse of the front, even leaving out the flat chasing. Even if it were a mirror image, I doubt it would really fit the sense of the definition. Most edges, reeding, gadrooning, etc. are moulded and applied. I believe you said this was not applied, so I pictured an ornate, and almost certainly a thin floral edge, usually associated with cheap, unsophisticated silversmithing. That is why I was so pleased to see the photos, and find we were discussing a quite nice piece. I would challenge you to find another example where someone calls that edge repoussee. I freely admit, this may be my definition, as the word is often abused. The flatware by Kirk, called repoussee, is not achieved by this technique, and never was, even in the early 19th c. Note I said flatware, as the holloware was originally repoussee, although today it is more likely to be drop forged. Also people call all that cast stuff put out by Hanau silversmiths, repoussee, a real abuse of the word. I hope you see what I am saying, in any terms it is a very nice piece.
Maurice

[dognose]

For a great example of the skill of the Chaser see the video linked from the post concerning Aidan J. Breen in this topic:

http://www.925-1000.com/forum/viewtopic ... &start=160

Trev.

[amena]

Hello Maurice
when I said that the edge had repoussé worked, I did not mean to give a decorative sense to the word, but only to say that the embossed edge is obtained by “pushing the metal in one direction then pushing it back the other way from the other side”.
The peripheral rim is certainly done by this technique

I don’t know if “repoussé” is the correct definition for this specific case, but the important thing for me is whether this type of work, however we call it, requires or not annealing, then the acid treatment, which would explain very well the higher values of fineness found in the edge. I think so.
Happy New Year to all.
Amena

[oel]

To anneal silver alloy; annealing is an effective method for re-softening silver alloys that have lost their ductility due to working or heat treatment. It permits sterling to be worked with reductions of 90% and even more. When the metal becomes too hard for further working, it is simply annealed and re-softened.
When silver alloys are annealed in open air, copper oxides will form. These oxides are of two types. The upper layer is cupric oxide, which has a black color; beneath the layer of cupric oxide there may also be another layer of oxide (cuprous oxide), which, because of its reddish color, is called "fire"
The black surface layer of cupric oxide can be removed by dipping the article in a "pickling solution"- a 5%-10% water solution of sulphuric acid. The pickling action can be accelerated by heating the solution.

After pickling, if a reddish layer is visible, it may be removed by polishing, but if it does not polish out, it can usually be removed by dipping the area in a cold, 50% solution of nitric acid. Since the nitric acid bath removes silver very rapidly, the operator must remove the article from the bath as soon as the fire is dissolved and rinse immediately with water. Any cloudy residue should be polished off immediately.
For the complete story see:
http://www.handyharmancanada.com/hbpm/silver/silver.htm

Oel.

[Francais]

Amena, that is absolutely repoussee work, and very unusual. I wish I had seen it earlier. The curled decoration showing is to be expected, unless the tray had been very thick, it would show normally. But the edge is very, very unusual. I must admit I thought there was a 50/50 chance that the border was applied and you didn't see the solder. But you are 100% correct in your description. I have seen that kind of border somewhere, but it wasn't memorable. Which probably means it was not a valuable piece. So I would be very surprised to find it on a piece of silver from France, Britain, etc. You can see that it is very labor intensive, and difficult to get right, any mistake would ruin the whole piece, which is the reason they used applied edges. It must be quite light. Very interesting indeed, which is one reason I guess we should never say "never" when discussing silver.
Oel, your description certainly describes the process better than mine. Although I don't remember hearing of the second bath or it removing silver. I didn't like using any acid, and had at least one accident, luckily not serious. I gave up trying to repair items, because of it. Subsequently I used pure silver, as I was only practicing techniques, and acid bath is not necessary with pure silver.
Maurice

[JLDoggett]

Is that edge possibly an applied piece of shaped sheet? You can tell if you can feel a gap under the edge on the bottom?

One additional step was done when making this piece. After shaping the sheet and raising the wall (anneal #1). The pattern would have first been chased on the upper face (anneal #2). After annealing the piece would be affixed face-side-down to a pitch board. The maker would follow the pattern of indentations on the reverse to follow for dapping up the raised (repousse) pattern (anneal #3). Next, after being sunk into a pitch bowl, the final chasing would have happened from the front to create the depressed areas in the foliage with a matting tool to smooth out the background around the ornament (the stippled pattern around the flourishes). Seeing pictures of both the front and back suggests the rim pattern was done with the same method and one would expect at the same time. Between each operation the piece would be completely annealed, to soften the metal and burn off any remaining pitch. This would have been done either with a gas torch or possibly over charcoal. Either way the silver with its thin coating of pitch would have given the piece a coating of carbon that would have helped prevent fire-scaling. In jewelry we call the process smoking a piece, coating a piece with candle soot to help prevent fire-scale. Lastly the possible edge would have been soldered into place. It would be this last soldering that could account for differing silver content on the surfaces on the piece...

Or - it could have to do with how the piece was finished which would need a whole page to explain the possibilities...

Or - It appears to be a provincial piece and may have been made with metal melted for other items. When alloying metal it is possible to pour the ingot before the metals have amalgamated completely and therefore the metal will assay differently from spot-to-spot though the average should be true to the stated quality.

[Francais]

I agree with all you wrote, except for two points. I think Amena is correct about there being no applied edge or solder. And secondly I presume if I understand the term "gas torch" it would be not be possible on an antique piece, and this clearly is antique. Perhaps I mis-understood. Otherwise it is one of the better treatments I have seen on this site, and I will have to take some time to digest all the new info in it. I wish you would take the full page to explain the first Or, here or somewhere else. I guess I would also like to know what you mean by "completely annealed", as my understanding is that some area can be annealed, where others are not, even using charcoal. Bravo!
Maurice

[JLDoggett]

By "applied edge" I am referring to what appears to be a flat area under the rim that appears to have some small dents and does not quite follow the contour of the rim. It is not uncommon to have ae applied under-edge to stiffen a thinner piece. If the edge was up-dented to thicken it as much as it appears (again the problem with photographs versus handling an item) then someone spent a long time doing the up-denting as opposed to the actual chasing and repousse work.

As for the complete annealing: it would be far easier and more practical to anneal the entire piece between steps than to just anneal the worked edge. Especially in a piece like this, applying heat to just the worked area would actually cause the center to become warped while an even over-all annealing would allow all the stresses to be relaxed and the piece stay as planned. The only time we ever annealed just the edge was with large butler trays where the ornamentation was on a very narrow band around the outer edge and even then it was not typically needed if the tray had an applied edge as the soldering of the edge would anneal the surrounding metal enough to do the finish chasing.

I should note that typically the finish chasing was not followed by annealing or heating as you want the piece to retain its work-hardened properties. The last process would be to carefully planish the underside of the bottom to work harden it.

I went and re-read the original article again and yes piece this predates gas torches by 40 years so it would have most likely been annealed over charcoal (a blow-pipe would not have been practical). The charcoal produces a reducing atmosphere helping to avoid fire-scaling.

As for the second OR... while the principles are all based in a desire to produce a specific finish on a piece, I have learned there are many ways to smooth and polish a piece of silver: from the use of fine garnet sand; powdered brick; metal files; or specific grit stones to smooth the metal; to the use of burnishers, powdered chalk; or metal oxides to produce a final finish.

I suspect I would be writing a book as I described the order and uses I have learned; In India typically they used finely crushed garnet mixed with oil to produce a fine mat finish then a wet burnisher to bring up a polished finish. Yet in Japan they typically used very fine wet-stones in diminishing grits to do the pre-polish with a paste of fine clay on a cloth for the final luster. Here it is typical to use a specific grit (commercially made) oil stone to finish the bottoms of pieces and power buffing machines with felt, muslin or leather buffing-wheels and oxides to achieve the hard luster of modern silver.

[oel]

Hi and thanks for the explanation, in one of my Dutch books about Silversmith Art it discusses a technique called; Bruneren or Burnishing, in combination with “white washing silver”(acid job) to create a “skin” (top layer) of pure silver. If I translate freely, it reads: acid washing an object made out of a silver alloy in combination with burnishing will leave a layer of pure silver at the surface of this treated object; the acid dissolves the copper in the epidermis (skin) of the silver alloy and the burnishing (forced rubbing) with Agate stone or burnishing tool and plenty of green soap will transform the epidermis into a very thin but hard layer of pure silver.
Some internet picks:
http://www.ehow.com/how_8125118_burnish-silver.html
http://en.wikipedia.org/wiki/Burnishing_(metal)


Oel.

[Francais]

Both responses are exactly the type of thing I like to see on the forum, very informative. I am lucky I didn't write what I thought earlier, as I thought putting the whole piece on charcoal would warp the bottom, not the other way around. Of course I have absolutely no experience, or very little. I raised a beaker once, just to better understand how much trouble it would be. I was fairly successful, to a point when I got lazy.
I think I had read about the thin layer of pure silver, but I can't remember where, it certainly wasn't in Dutch. I also was thinking of the more modern use of "dip it" to take off tarnish. Something auction houses are notorious for. My understanding backed up with observation is that the chemical re-deposits the silver oxide back onto the piece, which sounds great, but it leaves a surface without or with far less patina. Also of course it removes tarnish from the decoration, which in my opinion is a disaster. Of course as a dealer I have to use it on occasion, for salt disease etc.
Maurice

[JLDoggett]

Oel, that process has been used for centuries. I believe Cellini describes it in his treaties, though it was an old method when he used it. The same process can be used with gold pieces to produce the look of higher karat alloy. It produces a thicker layer than plating and usually holds up well to average wear. Its only problem is if the "skin" wears through you will get a colour difference in gold. In silver you get an odd patchy effect that can be helped by regular polishing until the "skin" is completely worn away. One other thing with the burnishing of the pure silver skin: pure silver does not tarnish so pieces finished this way do not develop the dark recesses that are in vogue today.

Francais, I know that feeling about chemical strippers. I only use them on modern chains, all the other silver I have in my showcases is hand-polished.

[Francais]

Well sometimes even antique pieces have to be dipped. Two examples come to mind. 30 years ago I loaned some silver for a museum exhibit, one piece had a tiny bit of salt disease. Then by chance the curator talked me into volunteering to clean silver. I was trying to polish out the salt spot, and the conservator came up and said the owner would have a heart attack, if they saw me doing that. I told her I doubted it, as I was the owner, but learned that a mixture of chemicals and polish works better.
The other time was more upsetting. I bought a French style candelabra, which I still use. They had been poorly dipped and lacquered. So not only did half the recesses not have oxidation, but the rest had to be dipped to make it even. I polished them the other day, they finally have the look I like, about 20 years later.