Sorry for the late reply gemw. I’m on the site a lot, just not the forum…and never noticed there was a little icon in the corner telling me about your reply ._.
I’ve gotten much better at finding optic signs! It was a matter of just practicing and persisting in looking in every corner of a gem (and making sure to use a loupe!) The magnification makes a huge difference in being able to see the interference colors. Now if only I had a third arm to hold everything…
I’ve finally seen real Brazil-law twinning in some quartz pieces I have too. The abrupt, geometric shaped interference is quite unique…but are there different patterns? I’ve noticed the amethyst pattern looks different from the pattern on my bi-color smoky quartz piece.