First, place the dichroic glass over a dark background. Then adjust your viewing angle until the surface reflection overpowers the dark background. Next, lightly touch the glass surface with a paper clip and you will see the paper clip reflected in the dichroic coating.
Here is the most important step... Does the reflection meet the paper clip, or is there a gap between the paper clip and its reflection?
On the coated side of the glass, the paper clip will touch its reflection. On the base side of the glass, a gap will separate the paper clip from its reflection. And, the gap will actually equal the thickness of the glass!
So, why is it important to know which side of the dichroic glass is coated?
Cutting - Always cut on the non-coated side of the glass. This helps to prevent chipping, especially on the heavily textured glass.
Coated Side Down - When using the coated side down or capped with clear glass, the dichroic glass will have a smooth glossy surface and sparkle like glitter! It will also change colors between the transmitted color and a completely different reflective color, depending on the angle of view.
Coated Side Up - Conversely, if you create with the coated side up or uncapped, the dichroic surface will have a highly metallic sheen. The piece may additionally be rough and textured depending on the type of dichroic glass you are using.
In the end, there is no wrong way to use dichroic glass... capped or uncapped, it's all a matter of choice. Actually, in my favorite workshop, we didn't fuse it at all! It's all about the experience... the more you know, the greater the range of effects you can achieve!