Hi all!
Thanks for the great comments, you've made my week!
To answer the questions on my orientation technique, I orient in full sunlight, marking with a white grease pen.
I started as a lapidary by hand (no machinery), cutting Aussie opal in my living room. So, I treat the orientation like opal, and go for the layers.
The photos here are from rough with a strong sheen. The strongest sheen will show easily when the cobble or boulder is dry, in full sunlight. However, orienting for slabbing should be done wet.
If you're working at night, be sure to use a full spectrum light, incandescent if possible, the brighter the better.
When orienting, "whacking" or slabbing obsidian, be careful to wear eye protection and good gloves (we prefer blue natrile palms and white, stretchy fabric from L*wes) and cover any skin you don't want to chance slicing open. Be aware that, if you work obsidian, you're going to get nicked or cut regularly.
The boulder had been "windowed" by whacking it with a 3 lb. sledge at a 45 degree angle to the sheen lines. The resulting "chip" will show much more of the surface of the line. We aren't much distressed by doing this, since we've got 3,000 lbs of obsidian!
About the "Aurora B" slabs:
These were slabbed parallel to (with, not through) the sheen line. The rough had an almost continuous sheen, with only the faintest lines.
In fact, this slab showed a bright fuchsia sheen while being oriented. To vary the effect, or accentuate the layers, saw at up to a 15 degree angle. Or, for a totally different effect when a piece has strong rainbow lines like the second slab, try a 90 degree cut
If you worry about accuracy, use a protractor or T-square. But, be aware that orientation is an art, and learned with practice. Generally, your optimum slab cut will be directly through the area of the least sheen.
Looking directly down at the brightest sheen, mark a dot in the center of it. Turn the piece and mark your cut just above the color line you want to feature, or in the case of solid sheen, at close to or right on 90 degrees from your dot. Marking several times around the piece will allow more accurate orientation.
Allow for your for chosen slab thickness. Be sure and allow for your saw blade thickness. If possible, use a finer grit continuous edge blade for the smoothest cut, since obsidian is brittle. An aggressive blade will create a much rougher slab, obscuring your sheen and costing you material.
After the first cut, clean the slab and examine it before reorienting and taking the next slice. If the boulder is in a vise, leave it until you've decided what reorientation is needed.
This will allow you to examine the slab, marking the angle with a line on the edge, parallel to the angle of the best sheen. Then, fit the slab back against the boulder, and turn it ( if needed) to get your best second cut.
A final word on saw safety; even if you use an oil saw, wear your gloves when handling slabs, or retrieving them from the saw tank. The finer the sawed surface, the sharper the saw edge will be. Remember, obsidian blades are still used for surgery, because the sharpest steel is dull in comparison.
About my photo technique:
The photos were taken using a Kodak 7.3 megapixel set to "Close Up" and at a distance of roughly 18".
Setting; On a rubberwood, waxed surfaced tv tray in the garden. The light colored wood contrasts nicely. Avoid having many objects in the near background, but also avoid drab backgrounds. Multiple colors in the background will assist your digital camera in recording the truest colors.
Wetting; I use a 10 second shutter delay, spraying the slab as close to the shutter release as possible. Wet is best!
Lighting; I photograph sheen & rainbow obsidian in the late afternoon to sunset light, to get the least glare and richest colors. Place you stand at an angle to the sun position, to avoid reflections. Photograph only in cloudless weather, since the wet slab will reflect any foreground objects.
Slab orientation; It's best to set your slab on a stand, at a slight angle from the sun. Adjust you camera position to capture the sheen, while avoiding glare & reflections.
[glow=red,2,300]Use a tripod![/glow]
That said, it's a testament to the high quality of the "Aurora B" slab that was hand held and
still showed incredible colors!
~
We'll be working on a video on orienting sheen & rainbow obsidian, which will be posted after our Club Show in October. Stay tuned!
Best regards,
Kris
P.S. Hey Susan! It's great to see you here! If you can wait on cutting that Peacock slab, I'll cut one of mine and post the results. This material is always an adventure!