Since I am assuming prior experience in the use of foiled glass, I will not explore the kinds, characteristics or availability of sheet glass.

My father started using dalles obtained from Blenko Glass and I have continued his practice. They are available in a wide variety of colors and are usually 12″ X 8″ X 1″ slabs of glass that are rough ( or textured ) on the bottom surface and smooth on the top and also along the edges.  Blenko will send you a sample set of the glass that they have on hand for a modest price. They ask that you call them directly for information concerning  availability, price and shipping costs since the dalles are not listed on their web site. The dalle in the following image is an example of my favorite group which runs from light orange to deep red in the central portion turning to various shades of yellow along the edges.

It is very important to be aware that the color of most of the dalles will lighten as the glass becomes thinner as the result of the faceting. It is, therefore, vital to explore how the color of the glass that you expect to use changes in response the amount of faceting you intend to employ.

This photograph above gives an idea how the color of two different dalles change as they become thinner, in general darker glass tends to maintains it color better than lighter colors.

All 6 petals of this flower were made from the same dalle with the color differences resulting solely from changes in the thickness of the glass

It is also important to be aware that the pigment in some dalles is not evenly distributed  throughout the glass and may even be concentrated along one edge as illustrated in the following two cross sectional photographs. You have to be careful not to facet away the color that you are expecting in your panel. 

One possible way to expand the color palate of the available dalles ( most are monochromatic ), that I would like to explore, is to use glass paint, frit or fusing colored glass on clear glass dalles ( I was told by Blenko that the C.O.E of the clear dalles is 90 ). This would allow one to obtain specific colors, color gradations, transitions or the addition of painted figures without the interpositions of lead lines. The only dalle, of which I am aware, that contains a transition of color ( orange/red to yellow ) within the dalle is pictured above. To accomplish this would require learning the intricacies of kiln work including the use of paint, frit, proper temperatures, soak time, annealing, faceting the glass before or after firing etc. If the details of this can be mastered it would allow for far more complex and detailed works to be executed using faceted glass. In 2014 I obtained a kiln inorder to explore the use of fused glass  see  the FUSED FACETED section of this site.