Ethiopian Welo opal is one of the most amazing opals on the market. The plays of colors often go completely through the whole piece of rough making it much easier to make a nicely shaped cut with absolutely amazing patterns and plays of color seen nowhere else in the natural world.
It has been a large topic of discussion, how to cut and polish Ethiopian opal. There is a lot of talk that this material is not stable and breaks and chips easily, an idea that was probably fueled by the nodule type Mezezo opals of Ethiopia that would often crack and craze. Welo opal is proving itself to be just as stable (in my experience so far even more stable!) as any of the finest Australian opals but often times much easier to cut and polish and has plays of colors and patterns unseen anywhere else in the world of opals. There are many schools of thought in cutting opal, this is just one way to do it. The best results come from experimenting, and adapting to your equipment.
First take caution on choosing the right piece of rough. If you hold the rough up to a light you can see any inclusions showing and how deep the pockets of matrix go. You can usually see a trend in the opals cracks and estimate pretty well how it is going to break or chip off. Welo opals crack most often because of small points of stress in the opal that eventually shift and break. These are usually seen immediately and you can deal with those any way you please. I myself like to help the cracks break by using a blunt knife or any steel object with a nice blunt edge and apply pressure to either end of the crack until it snaps, a lap saw works fine as well. A saw blade less than .012” wide is preferred, anything much larger can be more of a waste of this precious material than you might have bargained for. I've heard from some that you shouldn't use oil when cutting opals. This is especially true with hydrophane opals, as the oil has been known to be soaked up and kill the brightness of the stone.
Any finished Welo opal should be completely stable, fit for being set into a piece of jewelry and ready to be submerged in water and dried out every day without any harm being done to the opal. To many the hydrophane (base changing) property of this opal is one of the most amazing things about it and should be enjoyed as much as possible. This next step is one of the most important steps to getting a finished Welo Opal.
To get rid of any possible places were it can crack: Often times soaking the rough in water and drying them out completely once or twice will make that stressed point crack in the opal, if there is a stress point at all (never use heat to dry your opals). Sometimes for the first time getting Welo rough wet I like to place them on a wet paper towel for a day, so they slowly absorb water. I have noticed that sometimes when completely submerged in water the cracks expand a bit quickly and can “spider web” quickly through the opal. Introducing water slowly into the hydrophane opal will be much more forgiving to any points of stress and they will gradually expand as it naturally would, leaving you with that vulnerable point to have to deal with.
Unfortunately your gem may have turned into two by now, or you may have a smaller piece to work with but it is almost always a great surprise to see a whole new part of the gem exposed, often times it is much more impressive than what you were initially looking at. As any opal cutter knows, this is one of the greatest pains of cutting any opals, but by far the greatest reward as well, and it is this surprise that keeps us coming back to this wonderful material.
A finished Ethiopian Welo opal should be dried completely. After the stone is dried initially it will be completely opaque, it must dry to the next stage of turning back to crystal, sometimes they turn crystal clear and sometimes they turn less opaque. This can take a day or two or several months! You can watch the opaque “orb” in the middle turn clear with the outside coating. When the orb disappears all the water from the opal that can leave has left and the gem should be solid. I have yet to see a finished gem go through this entire process and crack later down the line.
Shaping and polishing Ethiopian Welo opals is largely up to personal preference. First off, I am hearing a lot of people talking about cutting there Welo opals dry. I find if you study your rough before and during the cutting process you can often see more to it than there initially was with water. For example, as the opal is getting wet the outside will turn crystal and the center will be an “orb” of opaque opal with color plays all around the opaque part. As that orb shrinks you can see what color play is going on precisely that deep in the opal by seeing the outer most skin of the orb, its like a window foreshadowing what your getting into… I’ve certainly found a few harlequins with this technique, and you can also see exactly how deep to cut when the pattern is at its prime. When I do end up cutting my opals dry it is just for pre-shaping, once I see exactly what I want and have have it shaped its time to fine tune and polish with the aid of water.
To avoid losing too much material and keep a nice shape to my piece I like to take my time with shaping and do as much as I can with higher grit diamond wheels than I would normally use with other material. I usually go through a progression on a flat lap pre-shaping with a very worn down 1200 diamond wheel, then go through a series of wet/dry sandpaper on the flat lap. I make sure each piece of wet/dry sand paper is well broken in before working the opal, or break it in on a spot I missed that the previous grit should have taken care of. The progression I go through is 320, 600, 1,200, 2,000, then use on muslin wheels 3000 grit diamond paste up to 14,000, and finish with the 50,000 for that beautiful “wet” finished look.
I have also seen great success going from 1200/3000 on a diamond wheel to cerium oxide or French oxide for final polish. The problem I have seen is working the hydrophane opal too much with Cerium Oxide will make an “orange peel” effect, where the surface is polished but has a grainy texture. In my experience it seems like the more hydrophane a piece is the more of a problem cerium oxide can be. I would recommend trying as many techniques as you have the opportunity to work with, as they will help you develop and create a style you feel most comfortable working with, and ultimately make the best cuts and polish possible.
Take your time with it and don’t put too much pressure on the opals. Getting a good polish is one of the hardest parts of getting a great finished gem. Work grits 600 and up very well, make sure the gem is completely rounded and every mark of the previous grit is worn out. Welo opals are soft, but they can take a bit longer to polish up than you think, but practice and patience should give you a good feel soon enough. Have fun with these and get to know the material. The more you work with opals the greater your eye for the material will get. Soon enough you’ll be creating aesthetically elegant shapes with plays of color oriented to make some unbelievable gems!
If you have any information or personal opinions about this topic contact me and I will, with your permission publish your thoughts on this topic here. There is a large handful of techniques to get to a finished gem and I would love to encourage as many as possible be known and shared. Contact me with any questions or comments you have on this topic and I’ll get back to you right away.