Diamond Glaze is a "dimensional white glue" (not a resin) so it will work fairly well when you want a domed
clear finish on top of something that's flat and contained. But since it is basically a white glue, its dried surface won't be as "hard" as some other clear finishes so will be more easily susceptible to scratching or perhaps to later cloudiness from moisture exposure.
DG (and similar brands of the same thing) suggests using something like a clear polyurethane coat on top of the dried DG to give more hardness and protection, and their newer version DG3 does dry a little harder but still not as hard as polyurethane. If your glaze is surrounded by a higher frame or something, that scratchability problem won't be as serious.
(Regular white glues are often used for clear coatings too if you don't need doming, like "decoupage mediums," or just regular PVA-white glues usually thinned down.)
A two-part clear epoxy resin (Envirotex Lite, e.g.) will also dome a bit on flat surfaces but not when the flat surface being coated is inside a taller frame ... in that case, the very top edges of the resin will stay on those framing "walls" when the resin shrinks its tiny bit and therefore the resin will actually be higher on the edges than the center area. If the flat surface is free-standing though (e.g., sitting on a stack of pennies or something) and the epoxy is applied slowly, the surface tension will allow it to dome a bit and the cured resin coating will end up with rounded edges.
Btw, the new "tweaked" epoxy resin called Easy Cast can end up somewhat flexible and with a softer surface than regular epoxy resins, esp. if it's exposed to body heat or any heat.
It can be good to put a coat of polyurethane on top of epoxy resins too, but less important than on dimensional white glues.
(2-part epoxy glues can work in the same way but are a little thicker, and some brands won't end up as clear --Devcon's 20 Ton 30-min setting one is good, I hear.)
Depending on what you're doing and the thickness of clear coating you want, you might want to use just plain polyurethane from the beginning or perhaps clear fingernail polish, or use one of the other possibilities (even a clear embossing powder like UTEE/etc, though has the same scratchability problems).
If you use a UV-resistant polyurethane like the Varathane brand, it and whatever is underneath it won't yellow if it would have otherwise.
If you want to read a bit more about dimensional white glues, or polyurethanes, etc., check out this page at my site (we use many of these things on polymer clay too, or on images in or on polymer clay):http://www.glassattic.com/polymer/finishes.htm
And if you want to read about epoxy resins (used as coatings, or inside "cells," etc), check out this page:http://www.glassattic.com/polymer/other_materials.htm