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Hey guys I know there are like a million treads on this subject but I was hoping to get some good quick answers and talk back and forth so I started a new one. I need to build an exposure box. I am planning on buying a replacement vacuum blanket for the top and using a medical vacuum pump I have handy. But as for the light source I think I am going to use B L tubes because it’s what I learned on. I know that Metal Halogens get the best detail and all but I know even less about those. I am still looking for good detail with the Black Light tube set up. Here’s the thing, how do I know what are good lights to use? What is it you look for? Strength rating, wattages ex. Obviously I am looking for non-filtered black lights and have been told that these are good, $7.78 F20T12BL 20W T12 24" BLACK LIGHT F20T12/BL INDUSTRIAL but I want to be able to know at an glance what I am getting. Thank you for any help.
 

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those bulbs will work fine...I use the same....6 about 5 inches from the glass...I get a nice halftone burn ...burn time is 11 minutes.

Inked

Mine are 4units of Toshiba FL20T8B/18 Blue. Burn my screens within 3 mins even with halftones.




Inked, do you get under-exposed if you burn your screens within 3 mins time with the BL?
 

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I have 6 20 watt black light bulbs 5 inches from the glass.....my burn time is 11 minutes which gives me a perfect solid 7 on the 21 step wedge test....I use a garden hose to washout the screens....if I burn less than 11 minutes I still get a good halftone and good stencil but I dont get a solid 7 on the 21 step test...I suppose I could burn for less as long as I get a good stencil...but I like to stick to the test wedge to find the burn time......

Inked
 

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Gave up on finding a stouffer here. Have contacted them directly and will order soon. Shipping costs thrice as much.

It seems that some of us are underexposing. One reason I think is lack of opacity of the ink in our transparencies such that exposures about twice the minimum time that it needs to get a reasonably good exposure results in some difficulty in the washout.

But for reference, do you use a gentle stream or jet?
 

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The two units I made, I had the bulbs fairly close together and about 3 inches from the glass. You want the bulbs evenly spaced, and closer will help yield quicker times. One used 6 24" bulbs, the other 10 48" bulbs, both with a vacuum top made out of pond liner from Home Depot. The vacuum top is almost essential for doing halftones.
 

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I am in the process of making a vacumm top......I have an old blanket off a 6 color offset press which is maybe 1/16 inch thick rubber..i will build a frame for it and hinge it to the lightbox.....hopefully it will be airtight......is there any tips in getting the top airtight?

@Angel - I washout my screens with a gentle spray with a regular garden hose.....I wet the screen and let it sit for 1 - 2 minutes ..this lets the water soften the unexposed emulsion...makes washout much easier and quicker....

Thanks

Inked
 

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I'm not sure a blanket from an offset press will have enough stretch in it to work well. Unless what you've got is different, the ones I've seen are pretty thick for the purpose, and have a fabric backing that would limit stretch. Even the pond liner, which is basically inner tube material, needs quite a bit of slack in it to pull down enough to draw the screen and film down tight to the glass. The best to use (and what the pros use) is the wetsuit neoprene stuff, but it isn't cheap and repairs are easier to make on the pond liner with a tire patch kit.
 

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have a fabric backing that would limit stretch.
I peeled the fabric backing off ..so it isnt as thick as it would be with it on...but you are correct there isnt much stretch to it even with the fabric back off......I will try it if it fails then I will get the pond liner.....

thanks for the input :)

Inked
 

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...

@Angel - I washout my screens with a gentle spray with a regular garden hose.....I wet the screen and let it sit for 1 - 2 minutes ..this lets the water soften the unexposed emulsion...makes washout much easier and quicker....

Thanks

Inked
Same here, 1-2 minutes on wet before washout.

There was a time that I use a nozzle and have to spray quite hard to wash out the unexposed emulsion. I was still using halogen work lamps then. At that time I often use the 2nd longest exposure that gave the best results on a step wedge test. Others used the shortest time. But sometimes, exposures using the 2nd longest time can be difficult to wash out unless with a heavy stream of water. I later use the 2nd shortest time that seems to produce good results. I have since removed the nozzle and use a gentle stream of water to washout exposures.

Based on your experience, it seems I won't be getting a solid 7 on the stouffer. I am ready to order the stouffer direct but frankly, I was thinking last night if the stouffer will be useful for us (or me). Maybe we are using much less opaque prints which causes some over-exposures leading to a moire difficult washout.

I hope someone with UV fluorescent (paging JSF) will try exposing at 11 minutes and see how it washes out. At the very least, we now have a basis to determine if our printers are producing opaque enough prints.

BTW, what is your printer and your ink? And are you using a RIP?
 

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I hope someone with UV fluorescent (paging JSF) will try exposing at 11 minutes and see how it washes out. At the very least, we now have a basis to determine if our printers are producing opaque enough prints.

Sir Angel, I have already made comment in regards from other threads that exposures having the screen burn overtime is no problem as you have a good print-out of positives and as the positive is securely fix to the screen.

Believe me, sometimes do I forget to turn of my lights in 10-20mins time and really never had a hardtime washing away the emulsion once it got wet.

If you wanted your emulsion to wash away easily, I wipe it sometimes with foam on running water and spray it afterwards. :)
 

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@ Angel -

I use a Epson r1900 printer with accurip all black system......the films are very dark ......I know if I expose for less time than 11 minutes the stencil is still very good to print with......but every where I have read says that you should receive a solid 7 on the step wedge for a perfectly exposed screen...so that is what I aim for....as I receive a solid 7 and the stencil washes away easily..so I stay with 11 minutes for my burn time.

Inked
 

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I have seen opaque prints at multiprint and I am sure a good printer will give very good opacity. But sometimes, there are other possible problems as well.

Earlier, when I was still using halogen, double the 5 min minimum time I need to get good exposure and I stand a good chance of getting an over exposure. I forget the details but I have difficulty washing out image at 7 or 8 minutes. I later attributed this to the illustration board I used to press the image down as posted elsewhere.

I am now using mercury and get good exposures in 1:15min. Triple the time or about 3:45min, depending on the image I still can get a good washout. I know because I started exposing at 5 minutes and move down to 4 minutes before I decided to use a step test calculator. I have been using the foamboard and foam I posted elsewhere since I started using mercury.

Others are having good exposure results with the illustration board though. I guess I do need a stouffer after all:D. That way determining the proper exposure time is left less to chance and film opacity, or lack thereof, (or influence of other factors) is more easily determined.
 

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I use a stouffer 21 step wedge strip on every screen...the light bulbs loose strength after time..so using a step test will tell you if your bulbs are getting weak and that you may need more time on exposure.

Inked
 
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