When you etch do you remove any backing paper?
No, laser burn right onto the paper (on the top)...then peel it away when finished...the paper is enough of a barrier to stop the beam from reaching the 'bottom' side of the acrylic and it just burns on the upper surface.
I wasn't sure how or if it would work but it did.
The other 'secret', if you want to call it that, is that the side you're burning on, becomes the back side of the plate when places into the LED light base. This means you have to mirror your text (BCL has this feature) when burning it in order to have it light up nicely when displayed. In other words, when sitting in the display, the burning is one the 'back side' of the acrylic.