15mins at 7 inches?? Did you have a fan blowing over the screen while you were burning it? More than likely you roasted your emulsion.
When I exposed with a 500W, I was at around 26" and unless I ran a fan, the glass would get pretty hot.
Emulsion should not get over 100F. At 7 inches, it was probably over 200F.
it seems like its two long of an expose i have a 500w light, i have mine at 15 inches high and burn for about 6.5 mins. i has been working great for me. good luck
Positive Failure
If the image area doesn't wash out, this usually means your positive failed to stop UV energy from reaching the stencil.
Dime Complete Opacity Test
To judge if your positive completely stops UV energy, tape a dime or piece of aluminum foil to the stencil to see if the dark areas of your positive are failing you and letting UV-A energy through to the stencil.
If the area covered by a dime doesn't wash out, you've exposed the stencil to UV or heat energy in storage, and the stencil resists dissolving with water.
21 Step Transmission Test Positive
The best stencil hardness test is a US$10 Stouffer 21 Step Transmission Gray Scale. A transmission gray scale is a small film positive with darker and darker filters next to each other in steps. When you have one on the stencil as you expose you will get a simulation of 21 different exposures to the stencil and you get visual feedback that shows you how well your stencil is exposed.
When you wash out the stencil, areas that didn’t get enough exposure will dissolve with water and go down the drain. You want a minimum of a Solid Step 7 that doesn't dissolve and go down the drain. More exposure will make your stencil more durable and less will make the stencil less durable.
When you put a gray scale on every screen, you will get visual feedback of the invisible action or cross linking and you will notice when it washes out differently and you will know your lamp or stencil is different and you have to change your exposure.
but could someone please just tell me a rough guide to using a 500 watt halogen flood with glass kept on and proclaim emulsion that works for them as I need to get printing quickly!,
When I exposed with a 500W, I was at around 26" and unless I ran a fan, the glass would get pretty hot.
take this advice and work with it.raise the light source to around 18 - 22 inches and have a fan blowwing on the screen while burning....you may want to decrease the burn time as well...I dont use that kind of emulsion but try to burn for 12 - 13 minutes and see if it helps.
but could someone please just tell me a rough guide to using a 500 watt halogen flood with glass kept on and proclaim emulsion that works for them as I need to get printing quickly!,
cheers!
If you would use the exposure calculator like previously mentioned you would waste 1 screen and have your answer in 15-20 minutes. There are too many variables to give you an answer, you can only be given guidelines. Like most things if you do it right the first time in the long run it saves you time and money.
but could someone please just tell me a rough guide to using a 500 watt halogen flood with glass kept on and proclaim emulsion that works for them as I need to get printing quickly!,
Need help with exposure time! 
Re: Need help with exposure time! 
