# Need help! Black light exposure time????



## eysakino (Oct 24, 2013)

4 units of 18w black light, 6 inches from the screen.

my problem is the exposure time.


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## sben763 (May 17, 2009)

No one can help you as you don't give enough info like your emulsion, you say black light I hope you have unfiltered black lights and not regular black lights available at most stores. 

Its best to get a exposure calculator and follow the instructions.


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## FullSpectrumSeps (Aug 2, 2012)

Exposure calculators don't really help either unfortunately.

The only thing that will help is to actually do test-exposures with film printed from your production output device, with a test of the details, solids, text sizes, halftones, etc that you want to find out.

I'm working on something that might be a bit universal for people to at least use printed out from their own printers as a more screenprint-friendly exposure calculator. Just a greyscale file that's already ripped at a high resolution, with various multiple LPI and DPI and angles of the gradients.... text and lines, etc.


The most critical part of the screenprint process -- the emulsion technology and method of exposure, film or stencil method with the density of the black.... all this stuff and its the most overlooked when companies are selling people on getting into screenprinting.


It is the main reason I don't offer freelance color separation services - there is almost no guarantee on the print-end these days with all the sub-par exposure methods going on, that people can consistently produce halftones.

I will push the fluorescent blacklight low-budget method to its limits to find out whether it can perform with blending and halftones, but I really think that there is just too much diffusion of the light going on, people have to expose too long, and the over-exposure of the details leads to not just issues with halftones, but even registering spot-colors... too much overexposure is like choking out the shape or text, and you're not supposed to trap to compensate those things, its all in the stencil-making.


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## sben763 (May 17, 2009)

Jeff good calculators are very helpful. They contain special UV filters in steps so that you can get very close within a few test exposures. The good calculators have halftones, text, and othe shapes and grids. Most just buy the cheap Stouffer 21 step calculator. I then take it a step further and use a microscope and check the edges as even with a calculator showing a step 7 can be under or over exposed. 

I had a 8 unfiltered black light unit for many years and could expose about anything. If you have the 4 bulb unit you will struggle with halftones as many have including me as I tried to help someone with a 4 bulb unit. Added 4 more bulbs, 2 ballast and they are working fine. 

I just went to single point MH and am struggling with dot gain because before the undercutting on the black light unit was perfect for on press dot gain with the exposure times I had nailed down by using microscope and calculator. Yes this part of the process is key. You can have the best press and film printer but if you can't make a screen properly nothing else matters 

Then there is dot gain from your printer in conjunction with on press dot gain. My films have never been a problem from day 1. Epson 1400 all black with UV dye ink, I print 100% CMYK and films are very dense. Now that I use a vacuum lid I get ink transfer to the screen and may have something to do with the extra heat but even with the transfer of ink I can still use the films at least 2 more times without worry.


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## 20vK (Jul 9, 2011)

Yup - I'm running an Epson 4900, waterproof roll film (from ryonet), all black ink, (right now black max, until I need to refill), and also get ink transfer. 1000W halogen, 3 min exposures on vacuum.

Even after drying both screen and positive with dehumidifier down to 35 rh.

I think it has a lot to do with photopolymer emulsion, which seems to suck moisture. Haven't used diazo for a while, but may well give it a run to see. Pretty sure it is a photopolymer thing though.

I found wetting the screen frequently and letting it sit in washout helps remove the ink...... Although I have lost halftones and subsequently ruined exposures from stubborn printer ink before. We can't be the only ones - there must be a solution. Was gonna go to fissons for film to try them out, but I guess you use them already Sean?


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## 20vK (Jul 9, 2011)

Unless we are laying down ink too heavy?


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## sben763 (May 17, 2009)

It is essentially too much ink. I use the fixxons as well as Ryonets R film and there is no difference on the ink transfer . On washout I take the white scrub pad and hit the ink and it removes it quickly thus not having to over wet the screen. I just tried diazo the other day and still got the ink transfer. I think the heat has something to do with it as the black lights exposure unit was a lot lighter on the ink transfer. Not matter its not hindering my screen making with the quick hit with the scrub pad. I was so use to undercutting with the black light unit I now have calibration controls set in my rip because I now get virtually true screens where as before I printed strait up and the under cutting controlled all the dot gain. After 7 years I still experiment and change daily. If you look at my YouTube channel sben7633 there is a video washout where I use the pad. Although no ink I did that video to show a member I could washout with hose pressure and very quickly. I think it makes the water absorb more quickly in to the un exposed emulsion. I haven't had a unusable screen in a long time, probably just jinxed myself.


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## 20vK (Jul 9, 2011)

Can you tame / control ink deposits with film maker?

Maybe I should go back to my accurip settings and have a play..... (and potentially save a bunch of ink)!

Looking back - when my halogen blew and I was down to 2 blacklights (and 40 min exposures with diazo), I don't remember and ink transfer issues. Perhaps I should get the holesaw to my workhorse exposure unit and screw a couple more fans to it!


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## sben763 (May 17, 2009)

Yes there is a calibration curve I use. It take 5% and is now 1.63% and so on. You can with accurip it has calibration controls but since I know your a MAC person not sure if there are differences the the windows ver. I could give you my calibration setting. I use UV dye ink from hotzone360.com. I tried all the expensive film inks and never saw any difference.


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## FullSpectrumSeps (Aug 2, 2012)

I think that it's just the exposure calculators are not really reflecting the same aspects of dots and densities as your actual film output device... so it doesn't tell you anything besides what you'd get with the same density as the exposure calculator -- even if you match up to perhaps a similar density to your films -- the color may be shifted differently.

I'm going to start very low-budget, using the epson 1400 or 1430 in store-bought mode but probably printing 100% CMYK, I've seen this working to produce very dense films - some basic settings like for the paper and photo RPM mode etc. 

But the custom exposure calculator I make will help to do those things you mentioned Sean, like seeing what you get on the film (using a high-resolution scanner works great) - and then what comes out from the best timing and eom setup exposure and washout, you can scan the screen high res as well.. but its more about checking the final print let's say through a particular mesh and with a specific dot-pattern or the calculator sheet will have lots of various dot patterns to see perhaps mixing them up will be better.

But then you can scan the print in, for example black ink on a white shirt test-print... and start measuring those percentages you would use in a compensation-curve profile.

But the whole aspect of doing this is a scientific-method procedure, and it is only helpful to actually follow through with it precisely -- such as recording everything done for that print such as the settings from the printer, film used, emulsion, mesh type, count etc etc... you know -- but changing mesh, changing off-contacts, emulsion or the inks in the film, all of that can have an effect - especially in manual printing just the pressure or flood amount etc.. the ink consistency, on and on.

So, I have done these kind of measurements and compensations, analysis and color-management workflow improvements in a few large screenprint shops before as art director, pre-press technician/color separator, artist, etc... a lot of times just a 1-man art department thing, but a couple places I had a few other artists working with me and large shop with multiple output devices... one place we had the typical Xante screenwriter4, a nice OYO Techstyler, and two Sprite direct-to-screen inkjet printers with rip-stations.... each of these you can imagine all had a different way that halftones or details would resolve and end up on screens etc... especially the direct-to-screen, one was a newer model II, so obviously the older machine had a higher dot-gain just talking about when it lays the stencil image on the emulsion.

The techstyler was the best, dense and crisp 1200 dpi, doing RIPs in photoshop directly and outputting to that was a real pleasure.

But in my own startup, I don't have $12,000 sitting around to pay for a techstyler, HAH!

But everyone's setup is going to be different, and like I mentioned above, every variable that changes per stencil will make it different.

You can find out those curves through a lot of painstaking and scientific measurement, and apply them before the conversion to dots and yes it becomes like for specific percentages it is shifted before... but you can only compensate so much... if there is total dot-loss or gain in certain regions like too much compression, then stochastic methods with a particular size might be the only way for some, with a rather low-dpi.

But the exposure calculator should have all that stuff on it, and in things that work for screenprinters.. most of them I see are more like for off-set litho, with very fine details and high line-screen halftones.. and again done on a custom film with density.

Loving this discussion, I will check out your youtube channel, and I hope to be sharing my own videos soon too, where I don't just write about it anymore, lol.


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## PositiveDave (Dec 1, 2008)

try http://www.t-shirtforums.com/t-shirt-articles/t106506.html


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## FullSpectrumSeps (Aug 2, 2012)

PositiveDave said:


> try http://www.t-shirtforums.com/t-shirt-articles/t106506.html


I'm sorry Dave, but that is part of the whole problem.

That method does not tell you anything about halftone patterns.

It's only for solid spot-color stuff like large text and other designs... using cardboard or varying density of films, timing etc.... it tells you absolutely nothing about when you have a dark dense print but its in dot-patterns.

"piece of card" -- seriously?


I think it's part of the problem, not the solution.

But hey, for people who only want to print spot-color work that might work if their film-density from output device matches a piece of card. 

In my humble opinion...


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## sben763 (May 17, 2009)

A piece of card is to block out all the light not for any film density. I didn't even read his link but normally you would use your film and move that card every 30 sec thus is a very effective and true exposure test. If it was to use just a piece of card no film then not a real test

While I disagree and agree with you at the same time. 95% or better of all screen printer don't and will never get as technical as the other 5% or less of us. This is why some of us excel in the high end printing. Not to say someone can't do good work but every now and then you see a shirt that has that wow factor and that's not done without proper techniques starting from the artwork all the way through the press process especially on a manual things can change. 

We started out in this thread with a NEWBIE needing some help with more then likely a spot color design getting exposed and went strait to high tech. I think we need to start a thread in the advanced screen printing section for further discussion


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## FullSpectrumSeps (Aug 2, 2012)

I think that "Newbies" need to know the difference here.


I'm not saying they should know all the details of how to determine the capabilities of their equipment.. I'm saying that they should understand what a solid or large-open-area design is and anything that requires blending of the ink in that screen or halftones -- the capability limitations imposed by not being able to do any halftone blend screens.

Are halftone blends in a screen seriously considered a "high-end" thing???

It should be fundamental to any serious screenprinter. I know there are a lot of different business models out there, I'm not saying there are not plenty of operations successfully printing jobs every day that are all just spot-color stuff... but even those screens can sometimes get detailed with text or the way an artist designs etc.... its not just halftones, but even line thicknesses. 

I'm only advocating that there should be a little more intelligence about the exposure-testing people are doing, at least to help determine for most that there are simply these two types of screen-making capability --- the large-open-area stencil and the detailed or halftone blending stencil.... there is all sorts of technical break-down when discussing the aspects of each, and when there are mixtures of both on the same screen etc...

But I just don't consider the discussions of halftones or knowing how to expose a halftone screen as being "advanced" screenprinting. It should be basic introductory knowledge in making screens... I firmly believe even a "newbie" should be testing exposures with a full-on test pattern... the same test pattern would work for a startup printer or a seasoned professional shop.


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## sben763 (May 17, 2009)

I think your way over thinking this. Get some of your own experience of printing films exposing and final prints and you will see a lot of this just doesn't matter when it comes to 99% of all the customers. There are a lot of jobs I put out that I think I could have done this or that to make it better but when they are put in the customers hands and I see and hear the reactions and then I don't think any thing was needed. In 7 years I have not had 1 complaint and every reprint job that another company has done first have been told mine are much better. 

I definitely don't know it all and learn every single day. Sometimes that lesson is just that was a waste of time. Starting out I was always told with halftones I had expose less time then my spot colors. I have set times on my screens for 1 then mesh but 128-166 are the Same and 205-300 are the same and 2 the coating used. No matter whether its halftone or solid they are exposed the same time. Starting out I was told a bunch of crap that slowed and held me back like you can't do that type of job with your exposure unit you need a single point. Honestly I didn't have to worry about dot gain until I started using the single point. I've read and test tons of the experts theory's and a lot of them don't account enough to even waste your time on. Just my opinion of corse


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## FullSpectrumSeps (Aug 2, 2012)

sben763 said:


> Get some of your own experience of printing films exposing and final prints and you will see a lot of this just doesn't matter when it comes to 99% of all the customers.


LOL!!  You're funny man!


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## sben763 (May 17, 2009)

I know your experienced in the industry but have you ever set up your own shop of shop for someone starting from exposure unit to films and dialing in the equipment. I have several times. That what I was getting at. I wanted to clarify as I was just reading it looked like I was insinuating that you have no experience and I know that simply isn't true and have much talent. I know the majority of you talents and experience is in the artwork and separations. My experience in those parts is much less then yours. Where I have the most experience is screen making including calibration controls but only with a rip and I was recently told it can be done in Corel very easily and I'm sure in photoshop as well. And the actual manual printing. A good manual press printer can make or break a print and can make adjustments to make the print come out when things are off in the art department. The MM Campers print is a fine example of that.


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