The spirit drums from down under called to me from Solmu -
"Help, help".  | Quote: |  | | |  |
Originally Posted by Six |  | | | | | | | | | I have found my exposure table and can figure out calcs.
But What category would halogen light be under, been so long since science at school. | |  | |  | |
The sad news is: quartz halogen lamps are not recommended and not listed. You will notice the sun is also not listed or incandescent bulbs from your reading lamp. - or my father's old spotlight from the car.
It is your sworn duty as a screen maker to learn to make an exposure test. Spend $45 now and buy a $10 transmission 21 step gray scale and an exposure calculator from ANY emulsion manufacturer. Properly used they will last a lifetime and stop a lifetime of guessing. One exposure with a Stouffer 21 Step Gray scale where you hold a solid step 7 in the mesh, and you will know more than anyone else in the world what is going on in your shop. Looking back, would you spend $45 to have your 3 days and 3 screen back? With a gray scale, you can also tell people over the phone, what step number you are measuring with your scale and they will know what you are talking about. The scale has no friends. It will judge sun and halogen lamp the same.
More sad news, it's not good science to make one exposure, fail, and then switch to a completely different light source and start from scratch.
A stepped exposure test is just like learning to cook anything, from marshmallows to 6 course meals. You cook for a little time and then check, then cook a little more and check, then cook a little more and then check.
A slide show and a downloadable video are available at:
Support Menu of Screen Making Products
Download the direct emulsion video under the General tab.
You are also using a industrial strength water resistant emulsion that is not very fast, because to get that maximum water resistance, it has to be completely crosslinked.
The sun can be very strong, but it changes every 10 minutes and this afternoon it was cloudy.
Then you switched to a 200 watt bulb that has no promise of UV energy at all if it is incandescent.
Then you switched to a quartz halogen lamp that comes from a Mysterious place called "bunnings".
There are many variables, but exposure is easy to test. Search for "exposure test" in these forums.
You also need the ying to the yang of the exposure, the positive that is blocking the UV energy from cross linking the stencil so it dissolves with water and rinses down the drain. Yo must have a good positive. "Scrubbing? " There's not scrubbing out the image area in screen printing!
Emulsion is easy. If it rinses out of the stencil, it didn't get enough exposure to hold onto the mesh. If it doesn't wash out, something cross linked it and it holds in the mesh.
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Originally Posted by Six | | | | | | | | | | On the back of the lamps I want to use it says 2 x 500 watts. I was thinking of killing one ie using one pointed at the scource. I assume this means 1 is still 500 watts ie not 250 by itself.
anyway, what is the bulb classified as from this list. | | | | | | |
I have to guess that you bought a lighting fixture that is expected to hold 2 500 watt lamps. That means 500 watts of expensive electricity and plenty of WHITE VISIBLE light coming out, but UV energy is usually undesirable because is bleaches you girlfriends drapes and burns you eyes out over time, so manufacturers coat them with UV filters or filter the light with plain glass that does a nice job of filtering UV energy.
Search the forums for 'halogen'.
Often these lamps do put out SOME UV energy, but you could expect exposure times from 13 to 25 minutes. Only a test will tell.
925WR is a great emulsion, but when you pair it with low energy lamps, you have a slow exposing emulsion.
Search the forums for "925WR" for more comments on that emulsion.
In the USA, unless you are picking up the 925WR from the distributor, you are paying a 20 UPS hazardous materials fee because of the Mild, mild acid content of the syrup diazo sensitizer. Most hobby shops use TX from the Ulano product line because it uses powdered diazo sensitizer. Ulano also makes a much faster exposing modern emulsion called QT-Discharge. Don't let the discharge name scare you away.
emulsion + exposure newbie help 
