# Exposure Time Using Homemade 500W Halogen



## mkmicro (Dec 13, 2008)

Hi,

Here is my setup: 500W Halogen at 18" away, 20"x24" 156 mesh screen, CCI SWR Water Resist Dual Cure Emulsion, 1 coat on each side (1/1) using the thin side of the scoop coater - foam covered in black cloth under screen, waterproof positives, then glass on top of film.

I had some problems on the first exposure: 5 minutes - lots of washout of emulsion - figured it was under exposed.

Decided to do a stepwedge that I read on the forum - cover the screen and move it every minute.

I am up to 10 minutes and exposure seems close - but, I noticed two things:

1. The 8" x 11" waterproof film seems to leave an outline where it is placed on the screen (I still get a good solid sharp edge on the dark design)- I have noticed that the waterproof film is not crystal clear but a slight milky tint - should I expose longer?

2. The areas of the design that are washed out, after drying, have some areas that look like the water didn't evaporate - I could see through the screen - is this due to not getting all of the emulsion off (I did notice some slight runs on the screen). Would the ink push through?

Also, I am thinking that I may need to expose longer (only went to 10 minutes), as I did the test with 6pt font and the emulsion washed out of the fine print - expected that if I overexposed the area that I would start seeing the font not so nice and clean.

Thanks.


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## BroJames (Jul 8, 2008)

Using a 500w halogen set 18" above image, I can actually expose for 4 minutes using aquasol/murakami dual cure emulsion. That will be an underexposure but non-image area should hold on with slight hose pressure. 

10 minutes should be pretty close to the ideal exposure time although I have never exposed that long when I was still using a halogen bulb.

The outlines of your transparency may be due to when (or exaggerated by) your film turning milky or cloudy. This in turn is likely to be caused by excessive heat from your halogen lamp. try changing films or directing an electric fan on the glass. 

The thin film you see after the washout maybe due to under or over exposure. How prevalent and how "large" are they? They may be underexposure slime that find there way into the image area and dried there. But it is more likely to be emulsion that held on due to over exposure. Maybe exposure time is correct but you didn't see those "water didn't evaporate" during the wash out which is why they're there. 

Can you post a picture?


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## selanac (Jan 8, 2007)

I have the same setup. In fact there's a YouTube video on it. 12.5 minutes is what I use.


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## mkmicro (Dec 13, 2008)

Here are some photos:

Image 1 shows the stepwedge (minute markings) - my previous time exposure of 5 minutes shows clearly that I was underexposing the screen.

Image 2 shows the area of the waterproof film sheet 8" x 11" that I was mentioning on how the emulsion is affected by the film sheet.

It looks like I need to do another stepwedge test starting at 9 minutes as I did not see any overexposure on the 6pt font.

One other question: I am using a 1/8 inch glass that I purchased at a building supply - it is a glass replacement for a 16" x 20" photo frame - this shouldn't have any UV protection on the glass. Right? I didn't see any UV rating on the package or glass.


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## selanac (Jan 8, 2007)

Don't know if that glass in non UV or not. I was wondering if you used a glass or not. Have you tried putting an image on the film and exposing it for 12.5 minutes? If you coated on both sides you can probably expose for 13 minutes. 

I use my cell phone for the stop watch.


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## mkmicro (Dec 13, 2008)

I plan on doing the test again starting at 9 minutes and up. I need to know when I hit overexposure. I might end up purchasing the exposure calculator, just in case the bulb starts to age.


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## BroJames (Jul 8, 2008)

Starting at 9 minutes is fine but be sure to hit 13 minutes as Paul exposes for 12.5min. Purchasing a stouffer would be a good idea. Switching to a 250w mercury vapor lamp would also be a good idea - exposing at less than a quarter of the time at less than half the wattage.


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## mkmicro (Dec 13, 2008)

Is the mercury vapor the same as metal halide? Where would I find one (cost?)


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## mkmicro (Dec 13, 2008)

I found a great source on here: http://www.t-shirtforums.com/screen-printing-equipment/t112739.html

Explains quite a lot.

I am thinking of using a 400W Metal Halide Tube Unprotected (assuming that the tube needs to not be coated but clear).


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## BroJames (Jul 8, 2008)

Mercury vapor is different from metal halide although the later also contains mercury. Metal halide is preferred over mercury.


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## marcelolopez (Jul 16, 2007)

I expose for 14 min. the glass is 16 inches over the light.
It hasn't failed yet.
I use a timer as those used for bathroom fan, so I set the time, and leave it alone.
Sometimes I use the pressure washer, but most of the time with a regular sprayer it works.


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## selanac (Jan 8, 2007)

I found this link for a Mercury Vapor Light: H37KB-250 - GE HR250A37 - 250W Mercury Vapor Lamp Clear | ProLighting.com

This company also has a Metal Halide, buttom of page right corner:

Results for metal halide - Search - ProLighting.com

I've bought many light fixtures from Cheaplights, wonder if they carry the Mercury Viper or Metal Halide?


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## printworxz01 (Jun 11, 2014)

Good morning Guys

Just want to ask if what is the proper exposure time in my Exposure unit
here are my set up:
500w halogen lamp (firefly glass remove)
18" Distance 
Tulco Aquasol ER

1st attemp 5mins under exposed
2nd attemp 7mins Turn out Good
but on 3rd attempt 7mins looks like under expose again

im not sure if the no of coating affects the burning time

please reply


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## selanac (Jan 8, 2007)

I moved my light down to 12 inches, an expose for 3 minutes to 4 minutes depending on the Mesh Count. 200 Mesh count and higher is about 4 minute exposure. 

110 to 156 would be about 3 minutes. Have exposed hundreds of screens using this method.


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## printworxz01 (Jun 11, 2014)

Thanks for the reply bro, im using 120 mesh, still no good


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## selanac (Jan 8, 2007)

What kind of emulsion? Describe the glass you're using. How fars the light from the top of the glass?


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## phatdaddy (Oct 25, 2012)

Halogens ok, but really the wrong spectrum, so to get agood fast shoot you need to ramp up the wattage... I've got 1600 watts and 2 Blacklights and I'm getting good shoots at2 min. The residue is un cured emulsion. I blast my screens with filtered compressed air after. I also soak my screens like a film developer and spray with a water filled paint pot...


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## phatdaddy (Oct 25, 2012)

I almost forgot. Cooling. Halogens get stupid hot cooling fans are a must. As for the residue, you don't want that in there. Garment printing is pretty loosey goosey and you may get away with a little residue without it affecting print quality, but not decals or any other flat stock.


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## compustan (Mar 31, 2016)

works great for me also


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