# Use a projector to expose the screen?



## thunder (Aug 26, 2012)

I'm starting to print some t-shirts at home and I have a doubt.
You can expose a screen with a projector like that with 500watts? How long should I leave the screen exposed? Btw, I use diazo emulsion!










The instructions from my emulsion are right here: [media]http://www.serigraphie-boutique.fr/WebRoot/StoreLFR/Shops/62058141/Products/12/SunCoat_Horizon_YC4001_4005.pdf[/media]


One more question, can I add water to the powder diazo sensibilizer and use just a little part of it? Or will be damaged over time?

Thanks for your attention!! I would be grateful if you can help me!


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## Hegemone (Oct 18, 2011)

With that work light try starting with 20 minutes if it's about 18 inches from the scene. Screen, transparency positive, sheet of glass, then 18 inches then light. Get an exposure calculator strip and start using it on every screen till your dialed in to good exposure.


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## Hegemone (Oct 18, 2011)

Oh and take the safety glass out of the work light because it is built to filter uv out.


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## thunder (Aug 26, 2012)

Thanks!!But my screen is almost A2 size! I think 18cm its too close..
And I just have a screen..Will I have to spend all my emulsion just to test the exposure time?:/


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## superD70 (Dec 22, 2010)

18 inches, or 46 cm.
You need mix the whole bottle of diazo powder with water and add it to the emultion all at once, it will last at least a month stored in a refrigerator.
A exposure calculator is a small strip of film, you place it on a part of your screen away from your design to determine optimum exposure times, I use one on every screen I burn as dual cure diazo emultion exposure times change a bit as it ages.


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## thunder (Aug 26, 2012)

superD70 said:


> 18 inches, or 46 cm.
> You need mix the whole bottle of diazo powder with water and add it to the emultion all at once, it will last at least a month stored in a refrigerator.
> A exposure calculator is a small strip of film, you place it on a part of your screen away from your design to determine optimum exposure times, I use one on every screen I burn as dual cure diazo emultion exposure times change a bit as it ages.


Thanks for your help!

But, I read somewhere I can mix the diazo powder with water and then mix 1 part of it with 9 parts of emultion. Just the quantity I need to... Anyone have done that?


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## RichardGreaves (Nov 7, 2006)

thunder said:


> But, I read somewhere I can mix the diazo powder with water and then mix 1 part of it with 9 parts of emultion. Just the quantity I need to... Anyone have done that?


It's important to follow the instructions from your emulsion supplier.

I know you're looking for shortcuts, but when you're learning is the time to follow instructions.

Test on a small, paper money sized coating.

Distance is easy to calculate - You need even coverage so too close means too much intensity in the center. Too far means a longer than necessary time to cure your stencil.

Measure the diagonal of your image area and multiply by 1.5 for your suggested lamp distance.
http://www.ulano.com/FAQ/FAQexposure.htm#Q3

*Quartz Halogen Incandescent Lamp Homework*
T-Shirt Forums - Search Results

Don't be fooled by all the visible light and invisible infra-red energy that is ignored by the diazo sensitizer that only reacts to invisible UV energy. All that heat comes from electricity making the filament glow at around 1,000 degrees F. 

98% wasted energy.


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## sben763 (May 17, 2009)

Mix it all it's not worth that being a cause I you have problems. If you store it properly in the fridge most manufactures say 30-90 days. I've used 5 months with dual cure when I ran out of photopolymer and it worked just fine


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## RichardGreaves (Nov 7, 2006)

It's the water that breaks down diazo so that's why it has a short pot life. The refrigerator doesn't keep the water away from the diazo sensitizer.

Heat above 85 degrees F is the real enemy. If the ONLY cool place in your shop is the refrigerator your coating thicknesses will vary with temperature of the emulsion. 

Beware of the 42 degree F refrigerator. It's 10 degrees away from ice and will alter your coating unless you wait for it to return to room temperature.


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## thunder (Aug 26, 2012)

Thanks guys!!! I think you solved my doubts!

Btw, just let me know where can I get an exposure calculator strip..Preferably the UK...


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## RichardGreaves (Nov 7, 2006)

*500 watt Quartz Halogen work light to expose the screen?*



thunder said:


> Btw, just let me know where can I get an exposure calculator strip..Preferably the UK...



Darkroom Sundries from RH Designs
_*Near the bottom of the page*_
Stouffer 21-step (half stop) Sensitivity Guide (step wedge) *uncalibrated* (as supplied as part of our standard Calibration Kit)

*The Positive Expert I use in UK*
Dave at 
Positivity Limited
47, Wootton Bassett Road,
Swindon, Wilts. SN1 4NQ
Imagesetting Systems For Screenprint, Litho & Flexo printing









I suggest using a US$10 Stouffer T-2115 21 step gray scale to simulate 21 different exposures. A Stouffer scale is a 5 inch film positive with darker and darker filters next to each other in steps. This is a standard photographic darkroom test positive that's been used since the 1930's.


When you develop the stencil, areas that didn’t get enough exposure will dissolve with water and rinse down the drain. Aim for a minimum of a Solid Step 7 that adheres to the mesh and survives development. More exposure will make your stencil more durable and less will make the stencil less durable, but light scatter could start to choke fine lines or halftones.


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## Whit72 (Apr 12, 2012)

I'm using 2 500 halogens at 16 inches and exposing in 4:30 mins, I keep my emulsion in the fridge take it out an hour before I use it, no problems and its been in there for going on 3 months without issue.

Here's was my first screen

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## RichardGreaves (Nov 7, 2006)

Do you know what emulsion you're using so we can compare experiences?

What ink do you use?


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## Whit72 (Apr 12, 2012)

Speedball photo emulsion

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## selanac (Jan 8, 2007)

Throw the Speed Ball away. 

We use S.E.X from Performance. No mixing involved. A 500 watt Halogen shop light at 12 inches away for 3 minutes.


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## sben763 (May 17, 2009)

I'll second the S.E.X from performance screen. Also the shelf life on it is 1 year. Fine detail and halftone come out great even though it's photopolymer emulsion. Get one of the cheap $10-$15 exposure calculators dial it in and you'll never mix diazo again. I also use hi-FI from Ryonet which creates a thicker stencil than S.E.X emulsion but is very subseptical to humidity but also holds good detail but is more expensive so we only use when needed. Performance screen offers your first QT at 50% off.


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## SaB (May 15, 2007)

Speedball for me. 19" for 9min. With 500w flood light. Expose 16x20 screens.

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## patlew (Jul 10, 2012)

Also be careful of the heat that halogen light throws out. I have had emulsion overcure just from the heat. I use a fan pointed at the glass during burn period.


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## RichardGreaves (Nov 7, 2006)

Whit72 said:


> Speedball photo emulsion


OK, a diazo sensitized emulsion. 

If you use water-based ink, make sure you completely cure the stencil or it will break down.

But if you print plastisol ink, move to a faster pre-sensitized 18 month shelf life emulsion.


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## thunder (Aug 26, 2012)

Hi,
I've done the test from How to Determine correct screen exposure times using Vellum with a 1000watt halogene bulb about 65cm away from the screen.

I expose the screen for 8minutes. I divided the test in parts of 1minute.

That's my result..what do you think that's my perfect exposure time? 6, 7 or 8 minutes?

Thanks!!


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## selanac (Jan 8, 2007)

65 CM? that's like 25 inches away. Move the lite to 12 inches and cure in 1 to 2 minutes. 

If you want to stay with the same setup use 7.5 minutes.


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## RichardGreaves (Nov 7, 2006)

*Manual stepped exposure test on color changing diazo sensitizer emulsion*



thunder said:


> I've done the test from with a 1000watt halogene bulb about 65cm away from the screen.
> 
> I expose the screen for 8minutes.
> 
> ...


There is more to screen making than faster exposure times.

As I wrote in Post #7, it's easy to calculate the international standard for lamp distance. 65cm is the suggested distance for a 43cm *DIAGONAL *image.
http://www.t-shirtforums.com/screen-printing/t197841.html#post1163972

Closer is faster, but you will get different exposure power in the center compared to the outer edges. The angle the invisible UV energy strikes the stencil will undercut the positive.

Farther away means less energy so complete cure takes longer but, strikes at less of an angle.


*SR Test Positive*
Scott Ritter made a very nice test positive, but remember, any positive - or NO POSITIVE works when testing for complere cure of a diazo sensitized stencil. A manual stepped exposure means (in this case), 8 separate 1 minute exposures and you must sacrifice a stencil to get the result.

The great thing about slower reacting diazo sensitizer is that *it changes color* as it reacts with UV energy *UNLIKE* much faster pre-sensitized emulsions where I insist you buy a *Stouffer T-2115* Gray Scale to simulate 21 exposures with EVERY exposure - and never a wasted stencil. 

Look at the color change. When you don't see any further color change, there's no more diazo to react and any further UV exposure is wasted energy.

After 6 minutes, you've reached the saturation point of your stencil.

Did you take your picture from inside the screen?


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## Zenergy (Apr 14, 2011)

I'm using 2 500w shop lights about 16 inches away and ChromaBlue emulsion. Right now, I'm at around 2:15 for white screens and 2:30 for yellow. It's crisp and clean and everything washes out perfect.


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## Derbist (May 3, 2021)

Is someone using this technology now?


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## Timmirz (Jul 29, 2021)

Derbist said:


> Is someone using this technology now?


I am planning to use two projectors to increase productivity on new T-shirts. Now I am reading about how to connect two projectors at once. Designing an image for T-shirts gives an opportunity to improve the quality of handwork for the client.


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