I'm having some problems exposing my screens. When I've finished exposing them I can see the image burnt to the emulsion the way it should. When it comes time to wash away the emulsion after exposure it'll go alright for a while, the parts that need washing away will start to go, a little reluctantly perhaps; but they'll disappear while the rest of the emulsion looks pretty solid on the screen; but then the rest of the screen will start washing away too. The emulsion on the screen starts getting very slimy and soapy when water touches it.
I'm using a 500W lamp that I bought from Walmart for $12. There used to be a thick glass cover in front of it, which was blocking some of the UV light, so I've removed that. I've got the lamp 15" away from the screen, with a sheet of glass holding the transparencies against the screen. I'm using 2 inkjet transparencies stacked on top of each other. I've been exposing it anywhere from between 12 minutes to 1 hour and I've had no luck.
I believe the emulsion I'm using is Diazo. It came with the screen printing set that I bought.
I've got no idea what's going wrong; if it's the lamp or the emulsion. I heard soapy, slimy emulsion could be caused by under-exposure. I'm guessing they included some poor quality emulsion in the kit and that I'm going to have to throw it away and buy some more, but I thought I'd ask for help first.