Firing certain gemstones in metal clay is a very popular practice within the metal clay community. This article is intended to develop understanding and help you decide, "is this practice for you?"
Due to the fact that firing gemstones in place modifies the properties by "Heat Treating" the gemstone which can devalue the stone, we avoid promoting this practice.
It's important to understand that applying heat to any gemstone is considered heat treating the stone. Although this heat treatment has some positive intentional usage within the lapidary community, it's also associated with the deceptive practices of:
the creation of imitation gemstones such as Opal
misrepresenting the value of a gemstone based on color modification.
The properties of ALL natural gemstones are modified when heat treated. The changes in the properties can vary in range from:
enlarging / weakening of inclusions
making the stone more brittle / susceptible to chipping / breakage
Even fabricated gemstones such as cubic zircon are susceptible to property changes. The most common being the change of color which is related to the color additive used in the manufacturing.
"You can just lower the temperature to avoid CZ color change!" you say. Well yes, this MAY work, again depending on the type of additive used. Doing so will inevitable require a compromise in the quality of the metal after firing. This means a highly devalued metal quality along with devalued gemstone.
Within the field of fine jewelry making, these modifications should be declared to the purchaser. In many countries, this is actually a legal requirement. For example, in the USA this is a federal regulation covered by Commercial Practices-Section 16:
23.24 Disclosure of treatments to gemstones.
It is unfair or deceptive to fail to disclose that a gemstone has been treated if:
(a) The treatment is not permanent. The seller should disclose that the gemstone has been treated and that the treatment is or may not be permanent;
(b) The treatment creates special care requirements for the gemstone. The seller should disclose that the gemstone has been treated and has special care requirements. It is also recommended that the seller disclose the special care requirements to the purchaser; or
(c) The treatment has a significant effect on the stone's value. The seller should disclose that the gemstone has been treated.
Note to §23.24: The disclosures outlined in this section are applicable to sellers at every level of trade, as defined in §23.0(b) of these guides, and they may be made at the point of sale prior to sale, except that where a product can be purchased without personally viewing the product (e.g., direct mail catalogs, online services, televised shopping programs), disclosure should be made in the solicitation for, or description of, the product.
Although there may be some slight modification to the text, this type of regulation is in place in most countries, so it's worth checking locally.
So you create jewelry using meta clay including fired gemstones for commercial purposes. Ask yourself:
"Do I know the impact and property changes of the gemstone I used?"
"Do I know the value of the gemstone I used after heat treating it?"
"Can I inform my clients of the additional care requirements of the heat treated gemstone?"
Am I pricing my pieces taking into consideration of the devalued gemstone?"
If you do not have clear answers these questions, then albeit unintentional, you are misleading / deceiving your clients and yourself.
Remember, learning requires developing experience based on understanding & application of the understanding. This may not always be easy, but it will inevitably lead to growth, the mastery of skills and ultimately achieving goals.
The application of "opinion" creates experience fraught with pit-falls and disappointment. It may seem easy at the start, but inevitably leads to limited growth and disillusionment (disinterest).