Monday, 15 August 2016

Testing Art Clay Silver 950 Part 1

I was very excited when Aida announced a new Art Clay Silver product recently. Art Clay Silver 950. The Art Clay (AC) I have been using up until now is fine silver which hallmarks at 999. This new silver clay is what being termed as enriched sterling silver clay. Traditionally sterling silver is 925 - that means for every thousand parts 925 of them are fine (pure) silver and the other 75 are something else - often copper. The new AC950 is (as you've probably guessed by now!) 950 parts fine silver and 50 parts copper, so this is enriched sterling as it has a higher percentage of silver in it. This makes a silver alloy that is stronger than fine silver. The other real plus is that AC950 can be fired open shelf, no carbon involved!!!
I was delighted to be asked by Metal Clay Ltd to test out the new clay pre-release. The clay will be available from 1st September and you can pre-order on their website.
 Here is how I got on with it. lovely packet arrived and testing began :D
The clay felt slightly solider than AC999 on taking it out of the packet at first, but as soon as I kneaded it, it felt about the same as AC999. Rolling out and texturing were all very similar, drying took about the same length of time. It reconstituted well. Working with the dry clay it carved well and drilled well. If anything, to me it felt slightly stronger when working with the dry clay. MOST IMPORTANTLY baby wipes work beautifully with it for refining etc. Phew - anyone who knows me would know that would of been a real problem for me if they hadn't worked!!
I rolled out a piece of clay plain to .25mm thick and dried it naturally and the clay was very flexible. I cut some thin strips from the dry clay with scissors and it was possible to bend them into small links very easily. I didn't fire these as I only wanted to see how flexible the clay was.
Next I tried the same thing with a shallow texture on each side of the clay. This wasn't as flexible and broke easily on bending. This would need more testing to find the out the possibilities of using the clay like this.
I made a few small heart shapes. With any new clay checking out how the firing works is very important. Even though we were given a schedule for it there are always variables, not least the kiln that you use.
I fired just a couple of the little hearts first, and I made one using AC999 to fire at the same time. The firing schedule is from cold to 500°C with a 30 minute hold, then straight up to 870°C with a 60 minute hold. The instructions also say to leave pieces in the kiln until below 200°C. On my first pieces I did this. Here they are fresh out the kiln. You can see the difference in colour, AC999 in the middle and AC950 top and bottom.
 They seemed to fire well. I checked if they were sintered (fully fired) by putting a drop of water on the surface of each one. It stayed there nicely. If it had soaked straight in that would be an indication that the piece was not properly sintered. I also drew around the pieces before firing. This allowed me to check they had shrunk, another good indication of proper sintering. Then I bent one piece using pliers. It bent well and was noticeably harder to bend than the fine silver piece. The shrinkage on these little hearts appeared to be marginally more for AC950 than AC999. AC999 shrinks around 8%-10%. The packaging for the AC950 said shrinkage of 10%-13% so that seemed about right.
After these initial tests I wondered why the instructions suggested leaving the pieces in the kiln until it was below 200°C. If I was going to enamel pieces they would go in and out of the kiln at 800°C, so after that I didn't leave them to cool in the kiln. It could be there is a very good reason why they should be cooled in the kiln, but I didn't notice any difference by not doing it.
I fired the first pieces on ceramic fibre board and there was some slight marking on the backs of some of the pieces where it had stuck. I know my little kiln does run slightly hot so I fired the rest of the pieces at between 850°C and 860°C. There was still the odd bit of sticking on the second batch so after that I also fired on ceramic fibre paper. I think vermiculate would probably work well, but I didn't have any to hand.
For the next pieces I made a some more hearts and small ring. I made the ring at a UK size T.
After firing it had shrunk 7 sizes. After deformity correction I put it onto a mandrel and easily tapped up to a UK size N which is a shrinkage of 6 sizes. The band is 2 1/2mm wide and 1mm thick with a hammered texture that was rolled on when I made it in the clay. The stone is a 4mm lab ruby fired in place. The topper of the ring was attached to the band just using water and is really strongly attached (I hit it a few times with the hammer to check ;) ) The ring weighs in at just 1.45 grams!!! I was very impressed with this. There was quite a bit of distortion to the ring when it came out the kiln, but with the larger shrinkage that is to be expected really. It is very easy to re-round a ring.

As I often have my kiln running at 800°C plus when I'm enamelling I'm also in the habit of sometimes putting small pieces in to fire when the kiln is already hot. I placed one heart onto a hot kiln shelf at 870°C and put it straight back into the kiln just to see what happened. It was an interesting result! It went in flat and came out very domed! It also had less shrinkage. Whilst the water drop test seemed to show it was fairly sintered I suspect not all the binders burnt away so the piece had uneven shrinkage causing the curving. It is not something I would repeat!! ;)
I also tried to torch fire one piece. I used the torch to heat slowly to allow the binders to burn away first, and then took it up to orange and held it for 8 minutes. The piece had similar shrinkage to the kiln fired ones and appeared to be sintered. It bent to 90 degrees. This lead me to believe it might be possible to torch fire, but it would probably want a bit longer firing (maybe 2 x 5 minutes), and more testing to see if it would work on larger pieces.  
So...on to the crucial question...DOES IT ENAMEL???
The short answer is yes, but it is not quite that easy! ;)
I use transparent enamels all the time in my work. Opaques are generally less fussy and I suspect they will work direct onto AC950 but I haven't tested that. My tests are all using transparents :D
I did a several little test pieces first. In this photo are the results of different experiments.
Top left and middle right are direct onto polished AC950. The colours have changed and top left is going brown at the edges. The enamels colours should look like top right and middle left, turquoise blue and mid green. You can see they have really darkened when applied directly onto AC950.
Top right, middle left and bottom I added fine silver foil to the surface using the keum boo method. I didn't cover the whole of each heart, only part of it and you can see the difference. Whilst this might work on a plain piece I use textures all the while and it was immediately apparent this was not a viable solution on a textured surfaces. Because of this I didn't experiment any further with this idea.
Then  we come to the middle heart. This one has the same green as the other two in the middle row and the same red as the bottom piece.
Normally in enamelling we enamel on fine silver. If we use sterling sheet we either depletion gild or put the piece into nitric acid. The nitric acid eats away the copper at the surface and removes any firestain to leave a fine silver surface. I DID NOT want to use nitric acid - nasty stuff!!! So onto depletion gilding. This is a process of repeatedly heating a piece and then pickling it until the piece is bright white. The process creates a layer of fine silver up on the top surface of the piece, and this is what we want for enamelling. The middle heart was depletion gilded.  
Eureka! It worked just fine :D
Next I made  another couple of little pieces and depletion gilded them. You can see the flat heart and the bar are noticeably whiter than a piece of untreated AC950.
 All the colours again stayed nice and bright.
So would I use AC950 for enamelling? In some circumstances yes. It is horses for courses. If I can use AC999 for a piece I probably still will, but to be able to enamel AC950 after depletion gilding is a wonderful option where more strength is needed :D
Another thing I wanted to try out was combining AC999 with AC950. For this piece I made a textured backing of AC950 .75mm thick. I then made a circular textured piece in AC999 which was also .75mm thick. I attached the two together just using water. In the process of refining it I accidently broke it (oh sorry, make that - I deliberately broke it to see how well it would mend ;) lol). I again just used water to wet the breaks and the pieces reattached very easily. You can see the difference in the colour of the clays.
After firing and polishing the different colours are still visible. This also shows very clearly that the two clays do have different shrinkage rates (although maybe it doesn't show so clearly in the photo!) Where the AC999 is attached the piece has domed a little. I expected it to do that and I like the result.
Finally I enamelled this piece.

Today I've been using the last of the clay to make a couple more rings and another piece to enamel.  
I'll blog about those tomorrow!!! :D
If you've made it this far through the post - well done!!! ;) Go and have a cup of tea - you've earned it!!
Have fun!
Joy x

You can see the rest of my testing results in Testing Art Clay Silver 950 Part 2


  1. Love your work and the thorough testing of 'ACS950'!

  2. Thank you Joy for this extensive report! I'm looking forward to using this clay, when it arrives early September!

    1. Thanks Caroline :D I'm sure you'll love it!

  3. Thank You for this very informative post! I was wondering if you have any experience in soldering a piece of fired 950 clay to a piece of regular sterling silver and does this solder as you would regular sterling? Thanks! Angelica

  4. Thanks for that very informative post! I was wondering if you have any experience in soldering a fired, 950 clay piece to a regular piece of sterling silver and would this just be by using the same process for soldering? Thanks! Angelica

    1. Hi Angelica, yes you can solder a fired piece to sterling without any problems. Fired silver clay can be a bit more porous than sheet silver so if you burnish the area where you are going to solder that can help (although to be honest I don't normally bother ;) ) Best wishes, Joy


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