Why has this lady's question not been answered by Houzz? Plenty of time!

True stained glass can be both - copper foil with a glue type of backing on the foil is wrapped around each piece of the cut and bluff glass. The pieces will make a design or show an image and then each piece is soldered together which is an alloy of lead and tin and even of zinc.. Many times copper foil glass will have a patina placed on the solder to enhance the colors of the glass. These patinas are mostly acid base and may be in black, brown, different shades green, and/or silver. It gives the piece a universal flow and brings the pieces together as a finished piece. Foiled stained glass is to be used inside and not for outside use - of course many will put it outside but it will come apart in the future as the the copper foil glue backing with heat up and pull away from the glass pieces. Leaded windows like in a church or even in homes can take the elements and will not fall apart. Even leaded glass pieces are soldered together in the joints but are held togethe/sealed with a cement paste so that water and other elements can not leak or run inside of your home/window. Of course while lead is flexable most leaded windows will be encased with zinc on the outside rim of the leaded glass. Just remember copper foil is used in making stained glass projects just like leaded stained glass and it too may have a border of zinc to give it protection and for hanging purposes. I hope this answers your questions.