Monday, January 26, 2015

At What Temperature Does Sterling Silver Become Brittle?



In my last blog I tested temperature hardening sterling silver. It worked great! (For more information on temperature hardening, here is a link to that blog.) After completing the testing, a nagging question hit me. At what temperature does sterling silver become brittle? We heat it all the time with a torch, but the constant heat in a kiln must change its properties, making it brittle. We have all been told not to heat sterling silver in a kiln above 1300°F (704°C)  but my last test proved that at 1346°F (730°C) it was still pliable.

All of the tests were done with new scrap sterling silver sheet. I didn't want to keep using the same pieces as that could taint the testing. 

Test 1
First, I wanted to see if something about having the sterling silver embedded in metal clay caused a problem with it being brittle when heated above 1300°F (704°C). I embedded sheet and wire in-between two layers of PMC3. I also placed a piece of sterling silver wire in the kiln with the other two test pieces. I heated the pieces in the kiln at 1346°F (730°C) for an hour. I quenched each piece when the kiln's temperature reached below 500°F (260°C) All metal pieces are still pliable without breaking after bending 1-3 times, so it has nothing to do with the metal clay.

Test 2
I raised the temperature to 1366°F (741°C) and heated sheet sterling silver for one hour. It passes the bend test after bending it 4 times.

Test 3
I heated the sterling silver sheet to 1460°F (794°C) for one hour. It bent fine the first two times, but then broke on the third bend into two pieces.

Test 4 
I heated the sterling silver sheet to 1500°F (815°C) for one hour. It bent fine the first time but broke on the third bend.

Test 5
I heated the sterling silver sheet to 1500°F (815°C) for two hours. It broke on the first bend.

My assumption is there isn't an exact temperature when the sterling becomes brittle. As the temperature goes up, the sterling becomes more brittle and the longer the metal is heated the higher the chance of it becoming brittle.   

Test 6
I heated the sterling silver sheet to 1346°F (730°C) and soaked the metal with heat for 2 hours to see if a longer exposure to this temperature would cause it to become brittle and it did.

In conclusion, heating sterling silver up to 1346°F (730°C) is about the highest heat recommended, and only heat it for a short amount of time.

Addendum
Just after I finished writing this report, Linda Kaye-Moses emailed me with some great information. She uses the book, Theory and Practice of Goldsmithing translated to English by Charles Lewton-Brain as a reference book. She was kind enough to pass on this information.

Linda Kaye-Moses wrote:
"What you want to aim for as the final stage of working metal is fine grains, at the microscopic level. “Grain formation is only possible when the atoms are given enough movement energy in the form of an annealing heat so that they can leave their old position.” So, a work hardened piece must be annealed to return it to a more workable grain size. This temperature for sterling silver is around 200 degrees C (392 degrees F).

“If metal is heated for longer than is necessary, newly formed grains fuse together to form larger grains. The resulting large grains... affect malleability, so metal should not be annealed [heated] any longer than is absolutely necessary...Recrystallization structure [that is, the realignment of metal grain] is affected by annealing temperature...the minimum temperature required for the recrystallization differs for various metals. The more the temperature is raised above this minimum temperature, the faster the grains grow and eventually an enlargement of the entire structure occurs. Conditions that contribute to large grain formation are [pertinent to metal clay]: too slow heating when annealing; too high an annealing temperature; too much time at annealing temperature.”

Large grain structures in metal contribute to brittleness. “Large grained structures are unsuitable for mechanical deformation [like bending, forging, etc.] and have a tendency to crack.” When sterling silver is heated for long periods of time and at high temperatures (firing temperatures and durations for metal clay), it becomes brittle. “It is obviously desirable to...create the finest grain structure possible. To achieve this [pertinent to metal clay] heat it as rapidly as possible to the required temperature; Stop as soon as it is hot enough; do not prolong annealing time.”

“To age harden a silver-copper alloy, the metal is first annealed.” This is the first step you describe: Heat the sterling to 1292°F–1346°F (700°C–730°C) for 30–60 minutes. This annealing recrystallizes the metal, forming an internal small grain structure. “...then [the metal] is quenched...”, the second step you describe. This step makes the metal retain its small grain structure. The metal is then age-hardened as follows: It is “...heat-soaked (tempered) and allowed to cool slowly.” This last step is as you described...Heat the sterling again, this time to 572°F (300°C), holding at that temperature for 30–60 minutes.
It seems to me that the reason that ss metal clay becomes brittle, is that it is heated at too high a temp and for too long. Quenching does not alter the grain structure in this case. In fact it does very little to the metal.



Until next time, have fun claying around!



 
by Janet Alexander
Technical Adviser

Monday, January 19, 2015

Studio Set Up

Many artists think there is a kind of magic in setting up their studio space. Some think they need a special room, or furniture, or equipment. Some think they need all the fancy tools. Some feel the need to decorate. Others like to 'keep it real' and have a rustic space. I think you can set up a studio in whatever little bit of space you have, or even in a collection of small spaces distributed throughout your house.

Those great Ikea drawer units have also been discontinued.
My current studio is in an artist's co-op, which is housed in an old factory building. I'm very lucky to have found out about it when I moved to Richmond, Virginia a few years ago. My former studio was an Ikea desk in my tiny 350 sq. ft. apartment in Los Angeles. I was able to make that work because of a few modifications that I made.

First, I discovered an elevated bench pin, which makes sawing metal so much easier on your shoulder and elbow joints. Next, on a trip to Ikea, I saw a bin of under-mount computer keyboard shelves and thought one of them would be the perfect thing to use as a catch drawer! I put a towel on it so bits and files don't roll around. If I'm working with small parts or beads, they don't fall to the floor, never to be seen again. I think Ikea may have stopped selling the Summera shelf (which is a bummer because it was really inexpensive), but you could make one with supplies from the hardware store. An alternative would be to attach one side of a velcro strip to the bottom of your shop apron, and the other side to the underside of your desk. The apron creates a European style basin that collects sweeps (if you saw/pierce), odds & ends, and little fiddly metal clay elements that you may be sanding with buttery fingers. Next on my modification list is a magnetic knife rack designed for use in the kitchen, but when mounted to my studio wall will keep my small files and burrs neatly in place.
Click here if you'd like to see details of
this goldsmith's elaborate studio set up.

In addition to the metal smithing desk, I have another table for my metal clay work, one to hold my soldering set up (which I keep on a cookie tray and set on this desk when I'm ready to work - you can see a corner of it on the right of the photo above), and a high table for photography and to hold box tops of works in progress (so they don't get lost or broken). Harbor Freight has a couple of wonderful work benches if you want something really sturdy. Here's another one with an attached pegboard.

Metal clay artists don't do the same tasks as metalsmiths, so we don't really need a traditional bench (which is higher than a desk, so the artist sits lower to avoid muscle strain from leaning over to see their work), but I have to admit to craving one anyway. Until then, my collection of desks and adaptive tools & supplies will do just fine.


Posted by Lora Hart
Artistic Advisor


Monday, January 12, 2015

More Testing on Work-Hardening Sterling Silver



In my last blog post I wrote about how fine silver cannot be work-hardened. I also listed a method of work-hardening sterling silver by heating it in a kiln:
 
Step 1: Check the sterling for any solder joints that may already be present.

Step 2: Heat the sterling to 1292°F–1346°F (700°C–730°C) for 30–60 minutes; adjusting temperatures if solder is present (if low-temperature solder is present, heat the piece only to 1000°F–1200°F). Quench in water.

Step 3: Heat the sterling again, this time to 572°F (300°C), holding at that temperature for 30–60 minutes. After cooling, Vickers hardness will range between 120–140dph; if lower temperatures are used, the sterling will not achieve this level.
 

Someone asked me a great question, "if sterling silver turns brittle after heating it above 1300°F, why would this procedure not make the sterling silver brittle? Isn't this what we have all been taught, to not heat above 1300°F?" I set out to test the technique. 

Test 1
I heated a strip of sterling silver sheet to the highest temperatures in the above steps. First, to 1346°F (730°C) and held it for 60 minutes. I allowed the oven to cool a bit, and then I quenched the metal. I then re-heated it to 572°F (300°C), held the temperature and then allowed it to air cool. The results, very hard sterling silver sheet and not brittle!

Test 2
I heated another strip of sterling silver sheet to the lowest temperature 1292°F (700°C), held it for 60 minutes, allowed the oven to cool a bit, and then quenched the metal. I then re-heated it to 572°F (300°C) holding the temperature and then allowed it to air cool. The results, very hard sterling silver sheet and not brittle!

So, my next question is, "At what temperature does the sterling silver metal become brittle?"

I will continue my testing and report back!

Until next time, have fun claying around!





 
by Janet Alexander 
Technical Adviser

Monday, January 5, 2015

Profiles in Artistry - Monica Weber-Butler

British artist Monica Weber-Butler is a Facebook friend and recently posted a photo of a beautifully whimsical necklace she created. I was so enchanted with the construction that I had to know the story behind it. 'Bird Song' is so well thought out that I thought I'd share her process with you.  

The 2000 year old small fishing village of Beer, in south west England, has been my home for the past 14 years. Since the village sits in a cliff's crevice, the views of land and sea are spectacular, and since every road goes either up or down, perspective is ever changing. Out of my bedroom window, bird's nests are at
'Birdsong- Refuge for the Soul'
eye level even though they sit at the top of tall sycamore trees. Yet, as I walk down to my studio, I'm dwarfed by those very same trees! With seagull nests, the opposite is true: built high up among the chimneys - but at eye level as I walk down the steep roads. Time and again these sightings have made it to my sketchbook: page after page filled with drawings and doodles of leaves, branches, nests, birds and bird houses in all shapes and sizes. Moreover, my days are punctuated by bird song, from the optimistic dawn chorus greeting the new day to the soulful song of the robin redbreast bringing the day to a close, reminding me that it's time to finish up and go back home. Unsurprisingly, my "feathered neighbours" were the inspiration for this necklace.

Following are the steps Monica took to create the necklace. Click on the photos to enlarge them.

Birds, branches and nests:
I drew a few patterns to use as a guide when shaping the branches.  Each branch was individually sculpted/textured and tiny cutters were used to create the leaves, flowers and the perforations at each end. The body of the birds were sculpted, a tiny leaf cutter was used to create the wings, and an embossing tool (ball stylus) was used to mark the eyes. Once the birds were dry, a hole was drilled through the center of the body. The nests were made using a mold of a tiny acorn and a dapping tool was used to shape & hollow the PMC3 inside the mold.

The bird house:
I designed several bird houses and created paper templates for each of the components. Model railway texture plates were used to create the detailed tiled roof and wood plank walls. All the parts were textured, cut, shaped and allowed to dry, and were then assembled with water (I seldom use paste!) for a clean and sharp finish.

To create the clasp and other decorative elements, Monica used a combination of molds and stamps. The individual dangling birds were hand sculpted.

All pieces were refined in the leather hard stage, fired at 900°C/1650ºF for two hours, wire brushed and antiqued with liver of sulphur patina for a vintage look.



Assembling:
Long "V" shaped necklaces appeal to me greatly and I revisit that design time and again; they remind me of vintage pieces. The two main branches are a mirror image, designed to frame the bird house in the center. The other branches are arranged in different directions to emulate a tree and to create visual interest. 

Decorative moving elements:
Every nest was filled with three 2mm white freshwater pearls bound together with wire to form the clutch of eggs. Individual leaves, pearls, nests, a clutch of eggs, birds, and a branch were each threaded together with wire and carefully looped in place. Other components were wired directly to the branches.

The bird house has a bird and a clutch of eggs inside. The eggs were placed inside the house first, followed by the bird. A head pin wire was fed through the bird's back, the center of the clutch of eggs and the base of the bird house, and then looped onto the flower charm, thus enabling the bird to move inside the house.

Although the hustle and bustle of daily life can be overwhelming, when I wear the necklace I'm reminded of home, and I find a refuge for my soul.