Tips for cabbing Brazilian Iris Agate? UPDATE, new pics

More a matter of not cutting the slabs at the right angle. If the bands are oriented so they are not approximately at right angles to the slab, then any iris effect tends to get deflected and lost into the interior horizontally (just as it gets lost if the slab is too thick). If the slab was cut correctly for iris, assuming iris micro-bands are in there, then a low dome shouldn't much affect the display (and flat/tablet top shouldn't affect it at all).

There should be some indication of iris on a raw slab (by wetting it and holding it up to a light source). That's how you'd choose an area around which to design your cab. If there is not even a faint iris effect, I'd wonder how a seller would know in order to advertise it as "Iris"?

The microscopically fine bands actually are fine enough to block certain light wavelengths and let others pass through, depending on the angle. They act as a grating (sort of like polarized filters block out certain light waves). If the angle of the slab cut is wrong, then the light waves hit the boundary of another band, then bounce around (producing translucency), instead of some colors/wavelengths passing straight through.

Brazilian and some other Iris agates are cut from nodules, where the bands follow the curve of the roughly spherical nodule. In such material that does have iris, it is often only the centermost slabs that show the effect. As you slice further toward the ends of one of those nodules, the angle of the banding rapidly curves and the light going through those bands would be blocked or wrong to let light waves through. Maybe an illustration might help understand the difference between the bands in a center cut, and the blocking that gets progressively worse as successive slabs get cut away from the center...

Sorry for the blurry lines, just a quick drawing. There are probably better illustrations out there that explain the iris phenomenon.

Perhaps on some of it might be uncovered if the dome angle was just right, but more likely not. If this cab isn't showing iris colors at any angle, then perhaps flattening off the dome on a lap might find it. It is an attractive cab as-is, so perhaps not worth the risk.