Friday, January 31, 2014

11 Tips for Creating Bezel Settings for Cabochon Stones


Cabochon stones have a flat bottom with the sides rising up into a dome on the stone’s top. They are cut into a convex shape. There is a 90˚ angle where the bottom and the sides meet. The first 1-2 mm up the sides are at 90˚to the bottom and then the stone starts to curve over forming the dome.




The bezel setting holds the stone in place by coming just above the flat sides and folding over them right where the stone starts to curve into the dome.

The bezel is made of thin fine sliver wire.  Bezel wire comes in several heights and styles from plain to decorative.


When working with metal clay, the bezel wire can be embedded into the clay before sintering or it can be soldered on top of the metal clay after sintering.

Tips for Embedding Bezel Wire Into Unfired Metal Clay
  • Make the clay base the bezel is being pressed into at least five cards thick. If using PMC Sterling silver metal clay, make the base six cards thick, allowing for the extra shrinkage rate.
  • Choose the right bezel height. Allow extra height for 1mm of the bezel to be pressed into the metal clay. If the bezel is too tall, thin cardboard can be placed in the setting to raise the stone to the proper height. If cardboard can't be used (due to an opening in the base) then the bezel wire can be filed down to the proper height.
  •  Fit the bezel so that the stone fits loosely inside of it. This allows for slight deformation while sintering.
  • Cutting a hole in the base metal clay inside the center of the bezel helps keep the clay from warping while sintering. Allow for at least 4mm distance from opening to the bezel wire.
  • Filling the bezel with casting investment (the same material as ring plugs) helps keep the bezel from deforming during firing. If you have an opening in the bottom of the bezel, cover it with kiln paper and then pour the investment into the bezel filling it just below the bezel's top edge.
  • Adding decorative syringe or clay work around the outside of the bezel wire helps hold it to the base. 
  • Coating the bottom edge of the bezel wire with oil paste makes the join more secure.

Tips for Soldering a Bezel on Fired Metal Clay
  • The fired metal clay must be burnished in the area where the soldering takes place in order to close the pours of the porous metal clay.
  • Use sterling silver solder either, hard, medium, or soft.
  • If there is texture in that area, it must be smoothed in order to obtain a flush soldering join. It's best to smooth the area while the metal clay is in its dry stage. 
  • The metal clay's shrinkage must be accounted for so that the bezel fits the sintered metal clay. Create a drawing of your design in the finished size, including the location and size of the bezel. Scan the drawing and then print it larger according to the shrinkage percentage of the clay you are using. Use the enlarged drawing as your template for making your metal clay piece. It also allows you to know where not to have texture! Here are the percentages of enlargement for some of the different metal clays.
    • PMC3 and PMC+ shrinkage after firing at 1650F for 2 hours is 15%.  Enlarge the drawing on the printer/scanner by 118%.
    • Art Clay Silver - low fire shrinkage is approximately 9%. Enlarge the drawing on the printer/scanner by 110%.
    • PMC Sterling shrinkage is 15 - 20%.  It's best to err on the large side, so plan on the 20% shrinkage rate. Enlarge the drawing on the printer/scanner by 125%.  

by Janet Alexander
Technical Advisor


4 comments:

Babette said...

Janet - this information is worth it's weight in GOLD! Gee thanks.

Kris Kramer Designs said...

Thanks for sharing your expertise!

Janet Alexander said...

Thank you Babette and Kris! My next post will be about those problem bezels!

Caroline said...

Hi!
This article was really interesting to read! Can you tell me the temperature at which you fire the PMC with the fine silver setting embedded?
Do you use the minimal temperature in this case, to avoid warping due to shrinkage? or can you still fire at 1650F for 2 hours?
Thank you very much for your answer!

Caroline