Many people are attracted to shiny objects, so it’s only natural to want to set stones in metal clay. Some stones can be set directly into metal clay and fired in place, while others will have to be set after firing using more traditional methods. This article is an overview of the types of stones that can be set directly into metal clay and includes brief descriptions of some basic setting techniques.
Artist: Paula McDowell, Photo: Cool Tools, Marty Longrie
Stone bezel set after firing.
Artist: Meropi Toumbas, amethyst lab gem fired in place
Natural
Lab Grown
Always check the firing recommendations of each stone you want to fire in place.
Note: Don’t confuse hardness with durability when heating gemstones. The Mohs scale of hardness does not correlate to the ability to fire a stone
There are several stones that can be fired in place, but not all can be fired at the same temperature or using the same firing technique.
Natural corundum (sapphire and ruby) are very heat tolerant and are a good bet if you want to fire a natural stone, but diamond fired in the oxygen rich atmosphere of an open kiln will vaporize. Small diamonds have survived when buried in carbon, so the method of firing can also affect success when firing a natural stone.
High-fire stones that can be fired in place in an open kiln at 1650ºF (900C) for at least one hour without color change include:
Low-fire stones can be fired in place at temperatures from 1110º F (600C) to 1300ºF (700˚C) for at least 30 minutes. These are stones that are not only heat sensitive but may change colors at higher temperatures.
Some examples of these stones are:
No-fire stones are those that cannot be fired in place, either because the stone would be destroyed, or the color would be significantly changed. These stones would have to be set using traditional methods after firing the base metal clay piece.
Some examples of no-fire stones are:
Cool Tools, Nano Gems
Choosing a stone to set is just the first step to completing a design. Next, you’ll need to consider how it will be set into the clay. All stones need to be held in place with some kind of mechanical capture. In traditional methods, that includes prongs, bezels, or a combination of both.
When using metal clay, shrinkage must be also taken into consideration. Capturing the girdle – the widest part of a faceted stone – and accounting for the height of the prongs or bezel will take slightly more thought and preparation than when setting in milled or cast metal.
Parts of a Faceted Stone
The diameter of the stone at the girdle will correspond to the size listed by the vendor. (e.g. 3mm, 4.5mm, etc.) While this is an important factor while setting any stone, when using metal clay, a more important measurement might be the depth of the stone from table to culet. Faceted stones, whether cut by hand or machined will vary in depth, some will have steeper pavilion angles, and others will be shallower.
Digital calipers can help to measure a stone’s depth
There are two ways to measure a faceted stone to determine its depth.
1. Place the stone table side down on the work surface and stack thickness slats or playing cards on either side until it looks like they match the height of the stone. Place a transparent, flat object (like a Lucite coil/snake roller) on top of both the stone and slats and move it back and forth. If the stone slides with the movement, add more slats on either side until the stone remains stationery. Roll a slab of clay to that thickness in which to set the stone.
2. Using a digital caliper, carefully balance the stone between the jaws, then close them until the table is caught by the lower jaw, and the culet is pressed against the upper jaw. Read the resulting number and compile a stack of slats or cards to match. Use these to make the metal clay setting.
The girdle (the widest part of the stone) must be captured by the clay, meaning that the girdle must be below the clay surface. If the girdle is not below the surface, the stone will be pushed up and out during the sintering process as the clay shrinks.
Tip: To make sure the stone is set well, look at it from the side. The table should be perfectly in line with or slightly below the surface of the clay. If any of the crown facets show above the clay, push the stone down a little more
The simplest method for placing a fire in place stone in metal clay is simply to push it directly into the clay.
Artist: Julia Rai, push set fireable gem
Artist: Julia Rai, syringe set fireable gem
This technique makes use of syringe clay to wrap a bezel around the stone.
This is similar to the syringe method, except a coil is rolled from lump clay instead of extruded from a syringe.
Artist: Corina Gheorghe, Coil Set Stone
Artist: Lisel Crowley, bezel set fireable gem
The outer circumference of a slab bezel can mimic the shape of the stone or can be decoratively shaped with a cutter or template.
You can also use small decorative metal clay elements, such as flowers, leaves, granulation balls or syringe ‘vines’, that connect to the metal clay base and reach over the girdle of the stone to hold it in place. If using separate elements as prongs, space at least three (or as many as desired) so that they capture the stone securely. Or use two longer appliqués as partial bezels. Partial bezels do not fully encompass the stone, but still surround it enough to capture the stone securely.
Artist: Tracey Spurgin, Claw (prong) set rings
The outer circumference of a slab bezel can mimic the shape of the stone or can be decoratively shaped with a cutter or template.
Artist: Julia Rai, Glass cab held in place with silver clay balls
Artist: Stephanie Chavez, Glass cab set with sheet clay
Artist: Lis-el Crowley, Glass cab set with a bezel
Holes made behind stones are not just about light. When a pendant is worn against the skin, no light can get through. Unless a stone is elevated above a ring band (as in a Tiffany setting), no light can enter through the back.
When you make a hole in a metal clay setting it helps to decrease the amount of clay that would be displaced when pressing the stone into the clay (thereby distorting your piece) and it creates a portal through which to clean the stone. Lighter colored stones like aquamarine and citrine seem brighter, and tarnish doesn’t have a chance to develop and change the appearance of the stone.
This video shows the process of setting stones in metal clay.
This video shows the process of cleaning up a stone before firing.
As with most metal clay skills, it may be best to begin with a simple setting using fire in place stones which are embedded directly into the clay. Once you have mastered this method, you can move on to other approaches to set stones. As your understanding of and skill with metal clay grows, you will discover more creative ways to use stone setting techniques to enhance your designs.
For more on natural gemstones and durability read this explanation from the Gemological Institute of America (GIA):
GIA | Understanding Gem Durability
For more info on Nano Gems read this article:
Interweave | Nano Gemstones by Lis-el Crowley
For an explanation of simulated, created, and synthetic stones view this page:
Jewelry Notes | What Are Synthetic and Created Gemstones?
For a list of heat tolerant gemstones check out the following links.
Cool Tools | Gemstone Firing Guide
Gem Resources (look for an Excel file)
Rio Grande | Natural Gemstone Firing Guide
Artclay Silver | Natural & Synthetic Gemstone Firing Tests pdf
