|
|
Post by stardiamond on Aug 17, 2020 14:03:16 GMT -5
My only experience is with Koroit and this material is different. I imagine it is soft and could be flattened with an end lap. Depending on the shape you want there are templates with small shapes.
|
|
gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,063 
|
Post by gemfeller on Aug 17, 2020 14:04:46 GMT -5
Opal cutting is a complex topic. Welo opal happens to be one of the easiest types to orient correctly because play of color generally shows from every direction. One of the big problems is that it's usually encased in gray matrix which must be removed before a judgment about orientation can be made. I usually do it with a Mizzy grinding wheel in a Foredom (wear a dust mask!)
Once the matrix is gone orientation usually is a matter of simple geometry: deciding how to achieve the best yield by placing the bottom where the largest finished stone can result. Color orientation is also a major consideration in that decision.
Welo opal is a type I call "reverse hydrophane." It's thirsty and absorbs lots of water. In "normal" hydrophane there is no play of color before it's saturated with water, when it suddenly appears. Welo is just the opposite: its dry color play disappears when it's wet. It usually appears again when it dries in hours or a couple of days, but sometimes it fractures in the process. It's a bit of a gamble.
Because the POC goes away when cutting it wet, it's important that the initial judgment about orientation be correct because at some point one is cutting "blind" and can't make course corrections.
The above is based on my personal experience with Welo and many years of cutting non-hydrophane material. I'm sure other opal cutters will chime in. Hope this helps.
|
|
|
|
Post by pauls on Aug 17, 2020 16:55:48 GMT -5
Forget templates unless you are making a cab for a specific piece of jewellery. You need to save every bit of that gorgeous stuff.
For slicing you need one of those really thin diamond blades, water cooled, they are cheap, only a few dollars each for small ones.
Grinding I prefer to use very fine wheels and go slow, coarser wheels can grind a nice stone too far in milliseconds.
Polish I like Cerium on felt or Tin Oxide on felt, Opal cutters generally use Tin. (tradition probably)
|
|
|
|
Post by hummingbirdstones on Aug 17, 2020 17:40:16 GMT -5
Most opals are cut freeform to maximize every bit of precious opal you can. I have only cut one Welo ever, and as gemfeller said, the color disappears when it's in water. Mine dried out, but came back very milky instead of the lovely, clear opal it started out as. Last time I wasted money on Welo.
YMMV though, and Vince cut one that came out of the same parcel and it was fine. It's a crap-shoot for sure.
|
|
|
|
Post by pauls on Aug 17, 2020 19:26:15 GMT -5
It doesn't take much sanding. If you are grinding with say 600, then sand with 600 to get the stone nice and rounded, then whatever you have. It really is not difficult to get a really good polish on Opal.
Something not mentioned yet is dopping, be very careful not to get your stone too hot when dopping, just warm should do. I am reluctant to say use glue because then you need to soak in acetone to unstick it and I don't know what effect this would have on Opal, I know oils kill some opals.
|
|
|
|
Post by hummingbirdstones on Aug 17, 2020 19:39:46 GMT -5
I use the standard stages as everything else on opal. I'll go up to 14K and sometimes 50K, depending on my patience that day. I use CeOx as a polish on leather. Once it's at 14k, the polish comes up in a couple of seconds.
|
|
|
|
Post by opalpyrexia on Aug 17, 2020 20:07:10 GMT -5
You've gotten great advice from all of the replies so far. Regarding dopping ... for smaller opals, in the range of up to a 10 to maybe 15 mm maximum dimension, I dop with 1/8" brass rods and superglue. When cutting is complete, I remove them by heating the rods for about 5-7 seconds with a small butane torch about a half inch from the opal. After about 5-7 seconds I pull the opal off. I have never damaged a single opal when using the torch, but I did burn my index finger on one that got too hot (even though that opal was just fine.) For larger opals I use wooden dops. You may find that you have some pieces or leftovers that have some color but which may be too thin to cut a solid stone. Those may well be great candidates for opal doublets. Here are my prior posts on opal doublets:
|
|
Nov 15, 2024 17:44:51 GMT -5
Nov 15, 2024 17:44:51 GMT -5
