Friday, April 5, 2013

Sterling Test: How Much is Too Much?

by Janet Alexander
Technical Advisor

Well everyone, we have come to the end of my testing of PMC Sterling. After pushing, pulling, kneading, bending, and prodding it for over a year, I think we have found out quite a bit about it! 

For my last test I wanted to re-visit a test I did in August on making flexible clay. If you would like to refresh your memory here is the link to that test.  Flexible Sterling Clay  

Questions I wanted to answer with this test were:
  • When is too much glycerin too much?
  • What does the clay look like when it has too much glycerin ?
  • What happens if there is too much glycerin mixed into the clay?
  • How much is enough?
  • Does the clay become stiff after drying for months?
I will answer the last question first. The flexible clay I made last August has been moved from one state to another, been left unwrapped, and tossed into boxes and unpacked. And now after seven months of neglect, it is still just as flexible. It didn't even get torn up from the move! 

In today's test, I took a 50 gram package of PMC Sterling and cut it in half giving me two pieces weighing approx 25 grams each.

I wrapped one up and put it away for later. The other I rolled out as thin as I could between a report cover and added seven drops (even sizes) of glycerin to the clay. Then I rolled it up into  itself mixing the clay, as shown in the August test. I added eight more drops to the  clay, with a total of 15 drops of glycerine. I mixed into the clay. 

This turned out to be too much glycerin. As I started rolling the clay into the thickness I wanted I noticed that it got harder to roll flat. I couldn't get it three cards thin. It had developed a memory of being in a lump and started recoiling just a little. As I forced it to lay flat it became bumpy trapping air in the clay. Take a close look at this photo. The surface looks like an orange peel. I cut a shape out of this clay to test fire.

Next, I added glycerin to the other lump clay, this time adding only five drops of glycerine. Its texture was smooth and I was able to roll it three cards thick without trapping lots of air. Here is a photo of both clays.

Clay with 15 drops
Clay with 5 drops
After drying I test-bent the clay samples. Both bent the same amount without breaking.

I fired them, per the manufacturer's instructions, to see how the final results differed. The clay with too much glycerin came out bumpy.

At the end of the day, five drops per 25 grams appeared to be the magic number for me.

I hope you have found these tests as valuable a learning experience as I have!


KENJI said...

Thanks Janet for these tests. Helped me from not ruining a good 25gr packet of clay. Thanks also for all the other tests that you have conducted in the past. You're a great source of info!


Janet Alexander said...

Thank you Kenji!

Anonymous said...

Very interesting. This explains a lot! I appreciate you sharing the knowledge.