The Glitter Effect on Silver Metal Clay

As I mentioned a few days ago, both of my pieces fired during the workshop exhibited the glitter effect known to sporadically manifest in silver clay. One piece had fine glitter that typically polishes right out. From the photo below, however, it's apparent that the crystal grain sizes on my glittery frame are very large.


Small particles of vermiculite are visible in the crevices. They appear to be wedged into place. I had to literally dig the vermiculite out of the filled interior of the frame, where it appeared tightly packed.


Over the last few days I've tumbled this piece with stainless steel shot for many hours, but failed to completely remove this extra texture.


Although fairly smooth and shiny in some areas, in places the piece looks slightly rippled. I suspect the temperature in the kiln was dangerously close to melting this piece.


My recent experiences with this sparkly effect has me researching the issue. This topic has been the subject of frequent discussion within the metal clay community, specifically how to get it deliberately or how to avoid it. Since metal surfaces were my specialty during my scientific research life, I thought I'd put together my personal views on what is happening in this situation, what might cause it or enhance it, and how it might be avoided. Necessarily I should add that I can't PROVE my hypothesis. As a good scientist I'm putting together my observations, trying to encompass data relayed to me from the experiences of others (but totally unverified by me at this point), and filtering that through my understanding of how metal surfaces behave.

As a prelude, let me state that I earned my doctorate in physical chemistry/chemical physics for studies on silver surfaces. In the course of 15 years of research, I used (among other things) atomic resolution microscopes to study metal surfaces and even published the first verified observations of metal atoms by scanning tunneling microscopy, thought to be impossible, but accepted after my work. In the course of certain measurements, I became an "expert," whatever that is, on growing atomically flat silver onto mica surfaces.

When silver clay sinters, the organic binder is combusted and then the fine metal particles adhere to one another. Silver metal in its lowest energy state forms a metal single crystal, with all atoms perfectly arranged. Given enough thermal energy and time, atoms on the surface of the original small particles in metal clay will migrate to the edges of tiny crystal domains and attempt to achieve that crystalline structure. Pores within the sintered metal, due to voids between the original particles, will slowly fill, and shrinkage will occur.

Small crystal domains have been clearly observed in SEM (scanning electron microscopy) micrographs of sintered silver clay, imaged by Tina Carvalho and published by the PMC Guild here. The rough surface of freshly fired silver clay appears white due to the scattering effect of these small crystals on visible wavelengths of light. When the surface is burnished, those tiny mountains are physically flattened, ruining the regular crystalline surface, but imposing enough smoothness to reflect light. However, reintroducing the silver to the kiln in a repeat firing will allow the crystals to start to grow again and return the silver to the white state.

By holding the temperature of the metal clay elevated for an extended time, expectations would be that the crystals would continue to grow in size, perhaps eventually reaching a size that would be able to reflect light coherently enough to observe macroscopic crystal domains, i.e. domains visible to the eye, with the appearance of glitter. Alternatively, since the mobility of atoms on the surface depends upon thermal energy, increasing temperature will speed that crystal growth.

Tim McCreight has speculated that the occasional observations of a glittery surface of freshly fired metal clay are due to growth of large crystals, perhaps caused by elevated temperatures or slow coolings, which seems consistent with the picture of microscopic processes presented here. However, some artists never observe such effects, even with extended times at elevated temperature. This posits the question: is something else involved, operating in some situations and not in others?

One possible explanation is the observation that artists who note this phenomenon were often (but not always) using vermiculite or fiber blanket to support the work. How would this material play into the microscopic process discussed here?

The composition of vermiculite is particularly suspect since it is chemically related to mica. The atomic spacing on the surface of certain types of mica provide ideal spots for growing atomically flat silver surfaces because it matches almost perfectly the desired atomic spacing for silver. Everyone is familiar with that eggshell corrugated foam -- balls pack so nicely into that regular array of holes. The mica provides exactly that template for growing crystals of silver. Thus, the presence of such templates can provide nice nucleation sites to induce growth of large crystal grains. Ceramic fiber blanket, like that used by glass lampworkers or ceramicists, may have similar structure, but that's pure conjecture.

So, my suspicion is that several factors affect the appearance of the glitter effect.

1. High enough temperature may allow the surface to move a lot. So overfiring at temperatures higher than the typical 1650 degrees would tend to increase the growth of larger crystals.
   
2. Long enough time at high enough temperature may permit the surface to move more and hence grow the crystals larger. This accounts for conjectures that cooling down slowly may be correlated with the glitter effect.
   
3. Extra assistance in the form of nucleation sites from vermiculite, fiber blanket, kiln shelves or other materials placed in contact with the silver may help form large grains more quickly than if there were no template present.
   

Thus, the irregularity of the situation that causes the glitter effect depends on the exact combination of these factors present, making different artists see the effect under different circumstances.

Right now, if I wanted this effect, I'd try putting the surface in contact with small particle vermiculite (to give good contact), overfiring, and holding for an extended time. Since I don't want the glitter effect, I'll try avoiding vermiculite, checking my firing temperatures to ensure they don't exceed 1650, and ramping quickly, holding two hours only, then quenching.

And I'll keep collecting data to help refine my scientific understanding of what's happening. This is only a working hypothesis, after all, and subject to change with the addition of new information.

Metal Clay Weekend Workshop with Kate McKinnon

My weekend workshop with Kate McKinnon was fun and informative. The topic of note was boxes and birdhouses, but Kate is a very open teacher and invited questions about any of her techniques.


We learned about many of the techniques detailed in her book "Structural Metal Clay," which I highly recommend, and more from her two upcoming books on mixed media and sculptural metal clay and DVD:

• treasure boxes to display a favorite bead or other treasure (I'll be thinking about those in the future)
  
• architectural construction for houses and birdhouses
  
• rings of many types: strap, heavy wire, rivet (for beads), stack, etc.
  
• tree branches and other work with wire armatures
  
• ball rivets
  
• making attachments
  

The only frustration I had with the course was a firing issue. Some of the houses, like mine that had openings, were filled with vermiculite for support. However, too much vermiculite meant the houses bulged like little balloons during shrinkage, even popping less than perfect seams. Beyond that, the kilns fired long (another experience of fire brick vs. baffle kilns to add to my data set) and too hot, giving time for crystal domain growth leading to sparkly silver. It's the analog of devitrification on glass -- hold too long at just the right temperature and the mobile silver atoms rearrange themselves into glitter. I know some people love that look, but I'm not one of them.

My bulgy birdhouse above has been hammered back to something approaching original shape and had its seams reinforced. Not too much glitter here.

Bits: a bird and blossom on a 10 gauge wire to form into a ring, a couple of big head rivets for later attachments, and another bird on a wire to insert into the birdhouse (there's a hole in the bottom that needs to be enlarged).


This small open roof house still shows the horrific glitter back. I've never seen an example this extreme, so I hope that all polishes out. The open roof accommodates one of my enamel-painted glass tiles, with a jump ring through front and back holes to keep it in place, but leave it interchangeable.


Here, I've straightened the walls (and the bottom after I saw the photo) and popped a glass tile in to show what it will look like.



I have more to show and more to do, but right now chemistry class is calling me.

Working on Paper

When life is just too busy to get hands on clay, it's great to have a sketchbook nearby. When even sketching doesn't fit into the day, at least I can go back and look at past ideas for new inspiration.

Here are a few ideas on my drawing board, literally.

enamel-painted beads with fuchsias and hummers and silver endcaps:



and a silver box bead with similar imagery:



a bird and nest piece in silver clay with enamel:



a constructed box:



The box is a perfect thing to consider as I pack for a two day workshop this weekend at Wired Designs in San Antonio. The topic is boxes and birdhouses, taught by the imitable Kate McKinnon. How serendipitous is that?

More Textures for Metal Clay

Yesterday my local metal clay group had a meeting to play with texture making. Although I had recently purchased conventional Speedball linoleum cutters and printing blocks, I'd yet to give them a go. With a bin of small blocks at my side, I doodled away, slowly getting the feel of the tools.



While more useful for deeper textures, it was quite possible to do very low relief. I'm excited about the prospects of multiple heights to the impressions in metal clay. That's one of the things that's both useful and frustrating about the other methods of making texture plates that I've shown: it's harder to do multiple levels. Carving blocks allow more options with easy access.


These blocks are all approximately business card size.

We also used two-part silicone mold mix to take textures from found objects: lots of shells, coral, buttons, picture frame molding, etc. What a perfect thing to do while sitting in the sunshine on a lovely fall day.

Original Textures for Metal Clay

Today I've been working on new textures for my students to use (if they like) on Saturday. Why do I leave these things until the last minute? I started ages ago and got waylaid on my mission to make tear-aways and photopolymer plates out of copyright free clip art and my original drawings.


Three easy ways to make unusual textures for use with metal clay:

1. Photopolymer plates -- use either copyright-free or limited-reproduction images from sources such as Dover, or make your own quick drawings. Follow my previous directions. I made mine with 2 minute exposures in the weak afternoon sun, and they came out great.
   
2. Tear-away papers-- low relief polymer clay transfered onto paper, or the remaining polymer for both negative and positive. Follow Celie Fago's directions in Jewelry Artist Magazine online.
   
3. Polymer clay texture plates -- roll a sheet of polymer clay and bake, then use linoleum or wood carvers to carve original designs
   

No excuses for using the same old textures, now! While I was at it, I dug up the textures I drew for bronze bells -- spring and summer. Here it is fall. I guess I better get going, if I'm going to have a year's worth of bells before the year is out.

More Bird Tree Beads

Over the weekend I squeezed in a few more bird tree beads. I'm experimenting with different base colors and finding that many of the colors I'd most like to use react with the silver glass. They all turn out looking "golden" like the two on the right, although they might have been rose or lavender to begin with. I tried etching another one back, only to find that the silver glass looks a surprising dark blue purple if etched down very far (not far enough to remove the brown, of course).


CIM Celadon, however, stayed true to color. I love this color, but hate how shocky the glass is. This time, as I turned on the kiln, I thought to pop a rod in and was able to use it rather than just having the end repeatedly shatter.

I'm prepping for a metal clay with glass class on Saturday and my son's sixteenth birthday tomorrow, so more glass beads will have to wait until after Halloween. Time to get serious and just do color tests first.

My Favorite Glass Creation

Soul Searching, my wall quilt shown in the previous post, incorporated dichroic glass cabochons at the centers of all the floating squares. I bought those as buttons, but clipped the shanks off the back. Being expensive, they started me thinking about wanting to work in glass. I'd always loved glass, but thought of glass blowing, with a workshop involving huge kilns and furnaces, beyond my personal resources.

When I found that bead-making only involved a torch and small kiln, I thought "I can do that!" After learning the basics, I started trying to put my own twists on the work. I admired electroformed beads, and identified with that process as another that I'd done in the lab. The first glass creations that seemed truly my own were the bird vessels, based on the miniature blown vessels I learned from Tink Martin. There was that attraction to glass blowing, but brought down to a personal scale. I started adding wings and heads and working on the bird shape, but kept the glass simple and usually sans any decoration. When I brought the electroforming in to add some surface design to the birds, I fell in love with the elegance of the pieces.


This Blue Copperhead Wren vessel was my personal favorite. The shape was balanced, the tail stopper was perfectly seamless to the line, and the frill of picot edging on the electroforming just perfectly accented the simple lines of the wings. Even now the photo gives me a little tingle. Good thing since the piece sold.

I love some of the new electroformed and painted enamel beads almost as much. It wouldn't surprise me to have one of those supplant the bird vessel as the absolute favorite, but