I do stained glass. You have to make sure that the flux is on the copper, then heating the place you want to attach the soldering material to works smartest. Also, if this is the first project, check the type of soldering you are using against the heat of the soldering gun. There should be a gauge to adjust. And if the room you are doing this in is cold, or the project area or air is cold, it will cool down faster, and less likely to stick strongly. Also, if you are sanding the edges of the glass, (or not), or using an oiled glass cutter, it is advisable to wash each peice of glass with dish detergent, make sure it they are completly rinsed clean and dried thoroughly before putting the copper on. When I put the flex on, I use a brush, and make sure that all the copper and even overlapping to the glass, the flux is on. If the solder still isn't sticking, you can put more flex on the copper. Make absolute sure when you are using these products that you have lots of ventalation!