Designing in PMC Sterling

The makers of PMC - Mitsubishi Materials, say that PMC Sterling shrinks 15-20%. As part of the process of releasing a new material their R&D department does exhaustive research and that research yielded this number.  So far, my calculations of my non-laboratory research tell me my flat PMC Sterling pieces shrink 15%.  My rings, for which I use size as the unit of measure, shrink 3 sizes if they are band rings and quite a bit less if they are washers (1 to 2 sizes from dry to fired).

I believe the reason they say 15-20% is because there are so many factors affecting shrinkage: size, thickness, firing conditions, kiln, etc.

I think if you want precisely sized rings, the best course is the one Hattie Sanderson is taking.  She is using her Hattie’s Patties (fire in place ring inserts) to enforce size and also making stainless steel mesh ‘cages’ to fire the rings in so that the carbon doesn’t get between the ring and the insert causing distortion.  Interestingly, a ring in a stainless steel cage is actually surrounded by air (in the cage) and then the cage is surrounded by 8-10mm of carbon.  You can read about Hattie’s method HERE.

Rings made in PMC Sterling can be up-sized on a mandrel, as well.

What I like best about PMC Sterling doesn't have to do with its longer working time or its greater strength. What I most appreciate about it is its influence on my thinking, on my direction;  where it's pushed me and how I'm now thinking about these materials, these metal clays.

diamond ring

I can certainly describe the corners the Sterling has pushed me around; I can describe how wanting to test its strength led me to openwork, or wanting to assess just how much better it is to carve led me to develop new carving motifs.  I can describe my realization that 925 clay, when dry, is a little messier to sand than the fine silver clays and how that led to my using the scalpel more than I do with fine silver.  But there's also something about the nature of the dry 925 that lends itself to the scalpel's blade more readily than the fine silver; probably the same qualities that make it better for carving; greater elasticity, less chipping, more flexibility.
Sand paper is messier than whittling, so if I can whittle, I will.  But as it's turned out, the whittling has taken me in a new design direction, a direction about which I am excited.


 


















These are a group of washer rings (no seam) cut with a long blade and a template that let me avoid the business of making a seam. The one on the top left is the start of the Diamond ring.  Once they are dry, I make a record of them with my copier.  
                                                                                
Then I annotate the ring images, both so I can remake a specific ring and to reinforce the shrinkage. 


















These washer rings shrink less than the band rings.  Washer rings shrink approximately 1-2 sizes.  I don't know why, but I remember noting a similar phenomenon when I was testing BronzClay.
In the upper right corner is the Diamond Ring, whittled down with a scalpel, ready for setting the diamond.
The lower left is the start of the carved washer ring. 


 

















Blisters and Firing Modifications
I have had one piece of PMC Sterling blister in the past year. Since then (3 months ago) I have slowed the ramp down in the atmosphere stage; I've done 6 firings at 500F per hour and now 6 more at 800F per hour to 1000F (hold for 30 min).  This is based on the theory that I may not have been burning the binder out sufficiently at the full ramp and that slowing the ramp down when air-firing may do so. 
After cooling, I transfer the pieces to a steel container and put them on 10mm of carbon, then I add more carbon until it is 10mm above the top of the piece.  I cover the steel container, put it into the kiln, on kiln feet so air can circulate, then fire full ramp to 1520F** and hold for 1 hour (or more if the piece is large or there is more than one piece).
I was able to sand and burnish the blisters away on the ring shank even though it was very badly blistered.  The blisters were not empty inside; they were more like bulges so they could be pressed/abraded down. It's strong and fully sintered and looks fine.

**KIlns vary!  It's important to know your kiln and how accurate the temperature is.  Check the temperature, and do a few test pieces before you invest lots of time in a piece.
 













Shrinkage: This is an openwork ring, dry and ready to fire. It's size 11.5.  When fresh, this ring was 12.5.  Freshly fired the ring is size 9.5.



                                         
                                                                                                                              
I have made many of these rings and have gotten this same shrinkage each time: 3 sizes from fresh to fired, 2 sizes from dry to fired.
It's important to note that because of the construction techniques I use, the dry to fired shrinkage (2 sizes) is the more accurate number.  

These 2 open work rings have 24k gold keum-boo on the inside.

A bit more on shrinkage:
Flat pieces made of PMC Sterling are shrinking 15% consistently. This stitched ring was fired as a flat strip, then bent around a mandrel and stitched.                     





                                                                                                                                                               


















This picture describes how I checked the shrinkage. The graph paper shape is the template I used to cut the ring out so it's the size of the ring in fresh clay (and 4 cards thick).  The similar shape with the purple lines running across it is the fired piece enlarged by 118% (enlarging by 118% is equal to 15% shrinkage).  These two shapes being the same size proves a shrinkage rate of 15%. 
[Here's why: 15% from 100% equals 85%, to find the size you need to end up at 100, you divide 100 by 85 and get 118%.]
                                                                                                                                                                                                                                                         
 

















These small disks were made by my apprentice, Erin M. Harris.  They were rolled at two cards.  She made a copy of the circles dry, ready to fire (the group on the right).  The disks on the left are fired and enlarged by 118%.  The two groups are equal in size proving that these small disks also shrank 15%.

The official shrinkage rate is 15-20% and as I've said, there has been some variation in my results.  However, the shrinkage seems to be consistent by type: Washer rings are consistent with other washer rings, but vary from band rings, which are consistent among themselves.

Hattie Sanderson and Janet Alexander have both done a great deal of research on PMC Sterling in the past year.  Janet keeps a blog HERE.

In this series of rings I am investigating shrinkage.  I am also using a group of techniques that work with, rather than against, the natural tendency of metal clay to dry out; developing a natural edge, tearing, chipping and just turning the other cheek while it dries.

2 Tips for working with carbon:
 

















 Pouring the carbon from 1 container to another, in front of a window fan (blowing out), will keep your carbon dust free. I do this after every 2nd or 3rd firing. 

 












6" plastic ruler is a great way to keep track of how much carbon you've poured: Pour 10mm of carbon as a base, place your piece on that and continue pouring the carbon until it's 10mm above your piece.

 

I have used kiln paper to protect delicate openwork designs from carbon so that carbon granules don't wedge into open work and distort it. 

July Home Classes are up!

If you are interested in a class, please let me know and I'll hold a spot. If you've already emailed me, your spot is saved! You can read more about the classes HERE.

July 14-17 Polymer Clay Bracelets with PMC Adornments
July 21-24 Polymer Clay Bracelets with PMC Adornments (first class filled so I added a 2nd class)
July 28-31 Making Rings in PMC Sterling

PMC Sterling Rings

Pictured here are a group of rings I'm working on for my upcoming CraftCast webinar on April 4th and for my pre-PMC Conference class. Mostly I'm enjoying the process of learning about another new material, its pros and cons, and how to best integrate it into my studio.

About the rings: They are all about the same size as this makes it easier for me to keep track of the shrinkage and determine if it's regular.

They are all 'open' because I haven't wanted to do this in fine silver clay and PMC Sterling seems a perfect opportunity. They are all carved because it's simply one of my favorite activities and PMC Sterling does it so well. I have discovered something: The drier the clay, the more it's likely to chip when carved. If you're carving PMC Sterling and it chips try giving it a "steam bath". By this I mean, put it in a hydrating environment briefly then carve. This might be 10 minutes but it depends on where you live, the thickness of the piece, etc. Don't overdo the hydration or it will get floppy and while this is good if you want to re-form the piece, it may make it too fragile to carve.

Once I form, refine and carve the rings I begin trying different solutions. I have a lifetime of pebbles and pieces, not to mention those I make, to house on the rivet wire that joins the two sides of the ring band.

I love working this way: On one side of my desk I have a pile of treasures I've collected or made over the years: rocks, beads, baubles and bits. On the other side I am making and carving ring shanks, the solutions for the orphans in the other pile, the 'bits' pile. The fun is in mixing and matching them up then sorting out the inevitable problems that occur when joining disparite materials.

This hollow form "flip ring" looks straightforward but actually depends on a tube inside the hollow form through which the rivet wire will go. Without the tube, the rivet wire would simply bend inside the hollow form. Fortunately the PMC Sterling's longer open working time serves it well for use with the extruder and the tube was easy to make.

Later this month I'll be posting examples of other rings that will be featured on the Craftcast webinar.

Holiday Sale!

I'm having a SALE through Dec 15th! Select pieces are marked down 10% in my shop (under SALE), plus free Priority shipping on ANY purchase using coupon code: HOLIDAYFREESHIPPING

Just added this new pair of Twig Earrings to my shop. I've also added more earrings and several rings.

'Tis the season!

Testing the new PMC Sterling

I am captivated by the new Sterling PMC; having worked with it since the spring, I want to write a little bit about my experience.

I’m thrilled to be able to say it’s very strong when fired and lovely to work with when fresh. Like PMC Pro, it has a longer open working time than other versions of PMC. When dry, it’s generally similar to dry PMC3 or Plus except it's much easier to carve with gouges. It carves smoothly without chipping, like PMC Pro and like BronzClay.

Sterling PMC needs to be fired in 2 stages, a brief air fire and then a carbon firing. This is more complicated than the needs of fine silver PMC and at first it loomed large as a drawback for me. As I began to appreciate its strong points, however, the double firing became a lot more tolerable.

What follows is a brief story of my experience with the material to date. My plan for the winter is to explore more open work, more ring designs, hollow forms, and larger kiln loads. To be able to rely on metal clay for the kind of strength required by this type of work is thrilling to me. I look forward to developing ideas that I have been reluctant to do in PMC and also reluctant to fabricate in sterling metal.

Five Rings in Sterling PMC:

Please note: The times and temperatures I used in the firings described here were part of my testing process. The times and temperatures described in the PMC Sterling insert are our up-to-date recommendations for firing.

All of these pieces were fired at 1000F for 30 minutes then 1510F for 45 minutes, in well used coal carbon. All were fired with approx. 10mm of carbon on all sides (ie not much carbon).

The first (corset ring, 4 cards thick) was fired flat as a strip then keum-boo-ed on the inside surface with two layers of 24k foil (the gold adhered nicely, although a few tiny spots resisted the bonding). Then the strip was formed into a ring around a mandrel, laced with wire, patinated and polished.

This bee ring was fired face down and in spite of the band being thin, it did not warp or slump. The bee is quite thin, but strong and unmovable with my fingers.

The bee was more challenging to keum-boo than the corset ring, I think because the corset has no texture on the inside.

There was some staining on the surface of the bee that seemed to repel the gold. I tried cleaning it off but I couldn’t get the gold to adhere to some spots. This type of staining, after the carbon firing, has not happened again. The fact that the gold adheres as well as it does to the sterling without depletion gilding or any other preparation is still a mystery.

I made the snake to test a thick piece and to try carving the sterling clay. It is superb to carve.

I made this ring to test strength in open work pieces and also attachments like the little balls, which I attached with slip. It did well on both counts. The ring is thin but strong and the balls are not coming off.

I fired this ring face down in the carbon with a piece of kiln paper under the cutouts and on top of the cutouts so the carbon granules would not jam into the cut out areas. This worked perfectly well although the ring itself is too thin to be practical. In spite of it being thin, it did not slump. I fired this ring with 4 other pieces; two hollow tubes and two flat pieces. All fired to strong metal.

(dry ring)

(ready for firing)

This cylinder is the first hollow form I’ve made in sterling PMC. The caps on the top and bottom are donuts (rather than solid clay). I did this to conserve material. The cylinder did not distort in the firing; next time I will make it thinner walled and lighter weight.

I’m experimenting with firing more pieces in the carbon. The cylinder was fired with 4 other small pieces: 1000F in air for 30 minutes then 1510F in coal carbon for 45 minutes. All pieces are strong and well sintered.

I'll write more as I experiment more and experiment I will. As with the BronzClay, and then the PRO, I look forward to discoveries I'll make bumping along in territory that is not entirely known. As with everything to do with metal clay the pleasure is in the pioneering (well, at least most of the time).

I look forward to hearing about your discoveries, as well!

I'm teaching a PMC Sterling ring class before the PMC Conference this summer. The class is full but please let me know if you'd like to be on my mailing list for upcoming PMC Sterling classes.

We have a Winner!

Thanks so much to all who purchased raffle tickets for my Helping Hand Pendant. I'm so pleased to announce that we raised $1940 and I'm going to make it an even $2000 and send it to the Craft Emergency Relief Fund [CERF]). All the proceeds will directly benefit Vermont craftspeople hurt by Hurricane Irene.

And the winner is...............Terry Palmer of Lafayette, LA.

Congratulations Terry and to everyone for giving a helping hand!