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Hey,
so i've tried to build my own exposure unit. I built a box and got some glass, and all i needed was some lights. i sort of made a fixture using and bigger fixture and cutting it down to size. there was three fixtures in there, and i first tried the black lights from home depot and when i went to go wash it out i started to see a little of it but then nothing. i tried all times with this. then i read about that they need to be unfiltered black lights so i ordered some off of topbulb.com and when i got them they were two different brands of light. one was kind of a blue color and the other a purple. i tried them in there and then it didn't really work, i didn't think they were bright enough. i have also heard that you could use just regular fluorescent bulbs, so i did some looking and i had this box of 5 bulbs that were the thinner type of bulbs, and it was bright. i tried and it worked, but it washed out a little too much, so we tried alittle bit longer and we tried longer and shorter and it didn't work. and i'm just out of ideas
it might be easier just to start over:)
thanks,
Andrew
 

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Hello.
I made the same sort of device. I laid a bookcase on it's back, routed out a groove along the edges and laid in a piece of table glass. Pet Smart has T4 20w florescent UV tubes for about 20 bucks apiece (for herpetariums).. I got all of the electrical parts from Grangers or Home depot. It has 8 bulbs spaced about 4" apart about 3" from the glass. I now do 190 LPI index separations and can hold 6 point Times Roman type just fine. Exposure times run 2 min 45 secs. No under cutting, no problems of any kind. The only problem was wiring a preheat switch. Also I use a piece of indoor outdoor carpeting with a weighted piece of counter borad instead of a vacuum frame. Really, works every bit as well as a point light sources I've used in three of the "pro" shops I worked as an artist for. :)
 

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Hey,
so i've tried to build my own exposure unit. I built a box and got some glass, and all i needed was some lights. i sort of made a fixture using and bigger fixture and cutting it down to size. there was three fixtures in there, and i first tried the black lights from home depot and when i went to go wash it out i started to see a little of it but then nothing. i tried all times with this. then i read about that they need to be unfiltered black lights so i ordered some off of topbulb.com and when i got them they were two different brands of light. one was kind of a blue color and the other a purple. i tried them in there and then it didn't really work, i didn't think they were bright enough. i have also heard that you could use just regular fluorescent bulbs, so i did some looking and i had this box of 5 bulbs that were the thinner type of bulbs, and it was bright. i tried and it worked, but it washed out a little too much, so we tried alittle bit longer and we tried longer and shorter and it didn't work. and i'm just out of ideas
it might be easier just to start over:)
thanks,
Andrew
Why so much work when yu can go to Home depot and buy a 500 watt halogen light
Set it 12-15inches from the screen cover with a glass plate and burn for 6 minutes.:)
 

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one was kind of a blue color and the other a purple. i tried them in there and then it didn't really work, i didn't think they were bright enough.

i have also heard that you could use just regular fluorescent bulbs, so i did some looking and i had this box of 5 bulbs that were the thinner type of bulbs, and it was bright.

The best fluorescent lamps for screen making are 40 watt Blacklight "BL" lamps. Remember that stencils only react to invisible UV energy so ANY light you see, is useless.

You could use just regular fluorescent bulbs, (what ever they might be), but they will never be as good as BL lamps.

With a lamp for graphic arts exposure performance, I would double check what TopBulb sent you. If they are both the same wattage and labeled BL they should be fine.
 

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Exposure with yellow safe lights?

I did basically the exact same thing as that guy except I use two yellow light safe bulbs instead of those fluorescent ones he uses

but other than that, I get a cure with the same emulsion in about 20-30 seconds
The suggested exposure for a fast exposing SBQ emulsion like Ulano QTX using a 1,000 graphics metal halide lamp on 305 mesh is 60 seconds, so I question what home made combination of 2 mystery yellow "light safe", bulbs can expose ANY emulsion in 30 seconds. I'm sure there is a misunderstanding here.

Yes, if you're printing plastisol, you can get away with the poorest screens on earth, so it may be working just fine for you, but it is a curing phenomenon - like a virgin birth.
 

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If you clicked the link and read the article, you'd notice that the fluorescent bulbs that I've replaced with yellow light safe bulbs are used for aligning the artwork.

The actual exposing is done with 6 F20T12 BL bulbs
 

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If you clicked the link and read the article, you'd notice that the fluorescent bulbs that I've replaced with yellow light safe bulbs are used for aligning the artwork.

The actual exposing is done with 6 F20T12 BL bulbs
Duh..that threw me, of course I didn't read the article, it jst sounded completely barking. :)
 

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Re: Exposure with yellow safe lights?

The suggested exposure for a fast exposing SBQ emulsion like Ulano QTX using a 1,000 graphics metal halide lamp on 305 mesh is 60 seconds, so I question what home made combination of 2 mystery yellow "light safe", bulbs can expose ANY emulsion in 30 seconds. I'm sure there is a misunderstanding here.

Yes, if you're printing plastisol, you can get away with the poorest screens on earth, so it may be working just fine for you, but it is a curing phenomenon - like a virgin birth.
Why is that?
 

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Why is that?

Why is that?
Plastisol ink is like salad dressing when it comes to attacking a stencil, but water-based ink, (made of 80% water) is made of the stuff that dissolves un-cured stencil like the Wicked Witch of the West.

The under exposed, raw, inside of the stencil will still be soluble (vulnerable / dissolvable), to the water in your ink - and it will breakdown as you rub it, over and over with your eraser like squeegee blade.
 

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Greaves, I got a question for you. With qtx , does stencil thickness affect fine line and halftone printing?

If so how, and what is the ideal stencil thickness for said reproduction on 110/156/230/305 mesh?
With ANY emulsion, stencil thickness must always be added to the mesh thickness to imagine what the end result will be. You have to be careful about the actual ink + dot + mesh tension + blade combination. Too thick, and the dots will look like skyscrapers and fall over.

Imagine your stencil could be taped to the bottom of your mesh and was as thin as aluminium foil - with perfectly drilled halftone dots. The deposit isn't really determined by the stencil, but by the mesh.

The tiny dots in a fine line or halftone need to be supported, so higher mesh counts are needed. The international standard for 60-65 lines per inch halftones is 305 or 330 threads per inch. Lower line counts can be supported by lower (thicker), mesh counts.


Undercutting from a rough stencil
With a direct emulsion, the UV light scatter from a high Rz surface makes the dots smaller and smaller as exposure is increased. This is why capillary film achieves the best photographic stencil.

SBQ sensitized emulsions are limited in their resolution abilities by the SBQ sensitizer. Dual-cure stencils are the best, but slower exposing because of the added diazo.

Halftone printing is sabotaged by low tension and soft blades. The best prints are low off-contact, high tension and sharp stiff blades.
 
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Re: Why is that?

Plastisol ink is like salad dressing when it comes to attacking a stencil, but water-based ink, (made of 80% water) is made of the stuff that dissolves un-cured stencil like the Wicked Witch of the West.

The under exposed, raw, inside of the stencil will still be soluble (vulnerable / dissolvable), to the water in your ink - and it will breakdown as you rub it, over and over with your eraser like squeegee blade.
To what degree does reexposure and hardener help?
 

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To To what degree does reexposure and hardener help?

To what degree does reexposure and hardener help?
Re-exposure is sometimes helpful for people with inferior exposing equipment. Hardener makes stencils permanent.

Re-Exposure
IF, you don't wash the inside of an underexposed stencil and the stencil survives, AND IF there is still sensitizer in the raw emulsion - it could still be re-exposed.

Don't post expose a wet stencil

If you choose to post-expose your stencil, make sure it's dry FIRST. Water will block cross-linking that might occur when you re-expose.

Underexposure
Plastisol printers use underexposure for halftone work because they don't understand UV light scatter or undercutting. Fine lines close up, or 'choke' - and they call that 'over exposure', so some people (especially plastisol printers), under expose and it 'works' with plastisol, but water-based inks aren't so kind. If you don't completely cure a water-resistant stencil - it can break down on the press.

Hardeners are designed to make permanent stencils
A chemical hardener shouldn't be used as a substitute for complete exposure cure. Depending on the chemical structure of the emulsion, you can get a screen that would survive printing, but it's no longer reclaimable.

Hardeners work best on a completely cured/exposed stencil.

The chemicals in a hardener treatment are used to fuse the molecules in an emulsion to make permanent stencils. A hardener treatment should be a last resort or a treatment so you can get another 50,000 prints from your stencil. If you're printing 70,000 prints, you can afford to re-mesh the frame when the print job is over.

Is it safe?
So, that's an answer on the purpose and industry standardized methods that will give you guaranteed results. You're asking for short cuts so you can skip the fundamentals. That's why I explain the background of fundamentals.

When you ask if you can, you're planning on leaving the approved path, and you're on your own. If you have trouble, we can't help you. That's why my experience told you to stay in the safety of the boat.

When you get out of the boat and look for a new path, that's one way cool new techniques are invented. This is how car and computer fanatics have cooler non-standard equipment than the average guy.

Now you should experiment. Good. When you're done, you never have to ask, "What happens if....?", and in less time than it took me to write this post.

Experiment
Put hardener on half of a screen you want to fix. You will soon know if it survives the job and then stencil removal.

When re-exposing a screen, cover half with cardboard and take it to the press. You will soon know if it survives the job and then stencil removal.
 

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In the normal course of exposure, it is easy to relate washout with underexposure and stubborn emulsions with overexposure. Are there other ways to go about this to ensure better exposures?

With regards to hardeners and reclaiming screens, Some of us used commecial reclaiming powder whihc we mix with water. Others use bleach. Others used other methods of course. However, there is a veteran printer here who apply hardeners and in his experience, it is easier to relcaim screens with hardeners using bleach. I am not sure if this is true for all hardeners. Just sharing.
 

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Exposure is at minimum, a combination of your positive, the stencil, the vacuum & the UV energy to expose the stencil.

Basic adhesion has to do with UV energy moving all the way through the stencil to completely harden/cure it. If it "seems" to be under or over exposed, you aren't measuring your exposure.

To monitor exposure, you should use a US$10 Stouffer 21 Step gray scale on every screen you expose for the rest of your life.
Exposure FAQ Screen Making Products how to measure exposure

Once you know how to completely cure the stencil - then you can focus on how to get fine lines to print. That's when you worry about using an exposure calculator.
 
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