I have been making a limited amount of custom cut cabochons for my jewelry designs for the last couple of years, but I have been toying with the idea of making custom intarsia cabochons which combine several types of stone material into a single cabochon. After researching the subject, I found that having a Flat Lap machine is key to getting perfect right angles on each piece of stone that is to be joined. Another key element to making this work is applying a proper backing material such as Jet, Onyx or Obsidian. Once again, this requires the use of a Flat Lap machine in order to get a perfectly flat back on both the backing and the joined material. Another issue to consider is the type of bonding agent to use, cure times involved, whether it will stay clear or yellow over time and how hard or flexible the bond will be between materials.
So being a bit adventurous, I decided to set out and give it a try. After using my Inland Craft 6” Swap Top Flat Lap, Loratone 6” lapidary grinding machine and a Gryphette glass grinder, I was able to cut some fairly passable intarsia cabochons. On the first one I used Jet as a backing material while it is easier to work with, it is a very messy material and basically gets on everything creating a black slurry when cut. After having to clean my equipment due to this, I decided to use some Black Obsidian instead, which does not suffer from that same issue. In the future I will use Black Obsidian, Black Onyx or other non-messy materials.
After cutting the various pieces and fitting them together, it was now time to assemble using a bonding agent. I decided to try 330 two part epoxy, which works well if you give it enough time to cure. The only problem I ran across was when I was cutting the surface of the cabochon down, it tended to heat up slightly causing the epoxy to soften and the brass strips I was using in the stone lifted out. I tried reinserting the brass strips using the same epoxy but ran across the same issue several times. So back to the drawing board. Next, I used a Cyanoacrylate to bond the various stone sections together along with the brass strips & backing. The bonds are almost instant, strong and do not require the several hours needed that the 330 Epoxy does for strength. This make this type of bonding agent perfect for stone intarsia and inlay work. It’s fast, strong, inexpensive compared to epoxy and does not yellow with age.
Cyanoacrylates are a family of strong fast-acting adhesives with industrial, medical, and household uses. They are various esters of cyanoacrylic acid. The acryl groups in the resin rapidly polymerise in the presence of water to form long, strong chains. They have some minor toxicity.
Specific cyanoacrylates include methyl 2-cyanoacrylate (MCA), ethyl 2-cyanoacrylate (ECA, commonly sold under trade names such as "Super Glue" and "Krazy Glue", or Toagosei), n-butyl cyanoacrylate (n-BCA), octyl cyanoacrylate and 2-octyl cyanoacrylate (used in medical, veterinary and first aid applications). The abbreviation "CA" is commonly used for industrial grade cyanoacrylate.
After trying a thin cyanoacrylate, I decided that using it for joining the sections together is best and that an industrial medium thickness gel would be great for attaching the backing to the sections as it would fill in any gaps that might be present. I ordered an industrial strength kit especially formulated for intarsia and inlay work, which works well as can be seen from the results shown. I will be offering many of these types of Intarsia and inlay cabochons for sale on the website in the very near future. That it for now and happy cabbing.