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Discussion Starter · #1 · (Edited)
Hi all,

I did a screen printing test that left my screen covered in emulsion that I can't remove. I'm not sure where I went wrong, or how many places I messed up, so here's what I did:

I used an emulsion scooper for the first time, so I did a shaky job of coating both sides. I kept the coated screen in several black garbage bags in my closet for a few weeks before I was ready to print. When I burned the screen, I put black foam under the squeegee side and pressed my transparent film down on the t-shirt side with glass from an old picture frame (I can't tell if the glass was UV resistant, but it was cheap so I doubt it?)

I exposed it for 10 mins, about 20 inches away from my screen, with a 250 watt bulb. When I went to wash out the emulsion, my image was barely there. I figured I would start all over, but now I can't get the emulsion off even with emulsion stripper. I've tried washing the screen with stripper twice, and blasted it with a hose.

Where did I go wrong with this one? Was my film not dark enough, or did I under/over expose the screen? What can I do to save my screen? Also, if you have an exposure calculator that you recommend to avoid this in the future, please link me!
 

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Yeah, we all started there :p

A key thing to understand is that partially cured emulsion remains reactive, and is subject to permanently locking in the screen. Things that contribute to partial exposure include: 1) Weak light source; 2) Too thick a layer of emulsion; 3) Emulsion that isn't thoroughly dry all the way through. #2 contributes greatly to #3.

To keep your emulsion layer on the thin side, use the sharp side of the coater. Emulsion needs humidity levels under 50% and some airflow in order to dry through and through.

All normal glass blocks a lot of UV light, because normal glass contains some iron (which is why it looks green when you look at the edge). Iron free glass is special purpose glass, and costs more; you will not accidentally have any laying around.

Do NOT waste entire screens taking random guesses at exposure times. Make a little test pattern with some small letters, larger letters, fine lines, thick lines, some halftone dots. Arrange these things in a group like 10" wide and 1.5" tall. Repeat that like 10 times down the film. You now have a test pattern (better than an exposure calculator, as it is printed with the same printer on the same film that you will use for all of your art). Get a heavy piece of black paper, or a piece of cardboard, and place it over your film so that only the first instance of your test pattern is uncovered. Expose that for an increment of time. Move the paper down so now the first two instances of the pattern are uncovered; expose for another increment of time. The idea is that the first instance of your pattern will be exposed for 10 times your time increment (if you have ten groups of the test pattern), and the last instance will be exposed for just one increment of time, and the others in between those two extremes. The goal of this first test is to get in the right ball park. Based on the results of this, you repeat the process with much smaller increments of time centered on the best exposure time from the first test.

You'll want to get a small, cheap pressure washer to assist in reclaiming your screens. There is no recovering the worst locked screens, but a pressure washer speeds up the process with normal screens, and can save marginal ones.

One other factor. If the art on your film is not blocking enough UV light, you won't be able to burn a good image on the screen. Laser printers are pretty much useless for making films for screen printing. Inkjets can get the job done, but it can take some tweaking of the settings, and it really helps to have film designed for this purpose (typical office supply transparencies cannot hold enough ink).

And last, a better cheap light source would be a 500w halogen work light. Take out the protective glass (it blocks UV). This is still a weak UV source, but much better than your 250w incandescent.

You'll get it sorted out! :) We've all been here, done that.
 

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Discussion Starter · #3 · (Edited)
Yeah, we all started there :p

A key thing to understand is that partially cured emulsion remains reactive, and is subject to permanently locking in the screen. Things that contribute to partial exposure include: 1) Weak light source; 2) Too thick a layer of emulsion; 3) Emulsion that isn't thoroughly dry all the way through. #2 contributes greatly to #3.

To keep your emulsion layer on the thin side, use the sharp side of the coater. Emulsion needs humidity levels under 50% and some airflow in order to dry through and through.

All normal glass blocks a lot of UV light, because normal glass contains some iron (which is why it looks green when you look at the edge). Iron free glass is special purpose glass, and costs more; you will not accidentally have any laying around.

Do NOT waste entire screens taking random guesses at exposure times. Make a little test pattern with some small letters, larger letters, fine lines, thick lines, some halftone dots. Arrange these things in a group like 10" wide and 1.5" tall. Repeat that like 10 times down the film. You now have a test pattern (better than an exposure calculator, as it is printed with the same printer on the same film that you will use for all of your art). Get a heavy piece of black paper, or a piece of cardboard, and place it over your film so that only the first instance of your test pattern is uncovered. Expose that for an increment of time. Move the paper down so now the first two instances of the pattern are uncovered; expose for another increment of time. The idea is that the first instance of your pattern will be exposed for 10 times your time increment (if you have ten groups of the test pattern), and the last instance will be exposed for just one increment of time, and the others in between those two extremes. The goal of this first test is to get in the right ball park. Based on the results of this, you repeat the process with much smaller increments of time centered on the best exposure time from the first test.

You'll want to get a small, cheap pressure washer to assist in reclaiming your screens. There is no recovering the worst locked screens, but a pressure washer speeds up the process with normal screens, and can save marginal ones.

One other factor. If the art on your film is not blocking enough UV light, you won't be able to burn a good image on the screen. Laser printers are pretty much useless for making films for screen printing. Inkjets can get the job done, but it can take some tweaking of the settings, and it really helps to have film designed for this purpose (typical office supply transparencies cannot hold enough ink).

And last, a better cheap light source would be a 500w halogen work light. Take out the protective glass (it blocks UV). This is still a weak UV source, but much better than your 250w incandescent.

You'll get it sorted out! :) We've all been here, done that.
This is incredibly helpful, thanks!! I have a few more questions for you:

Do 250 watt bulbs not work at all, or are they less effective? I unfortunately had to buy a pack of 250 watts and would hate to waste them, but I'll try to find a 500 watt online.

You also mentioned office supply transparencies aren't great. I bought transparency film for my inkjet printer, but should I get them printed at Office Depot instead? Or invest in some other type of film? I've seen people double or triple up their printed film, to get an opaque black, but it seems like a waste at $40 per pack of 50.

As for my screen, is it totally ruined? Or would another round of emulsion stripper with a power washer attachment help? I didn't understand how to use the scooper correctly and placed it flush against the screen, instead of using the edge. As you can imagine, the result was a gloopy mess! I'll post a picture, so you can get the full effect. 😅
 

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Discussion Starter · #4 ·
This is incredibly helpful, thanks!! I have a few more questions for you:

Do 250 watt bulbs not work at all, or are they less effective? I unfortunately had to buy a pack of 250 watts, and would hate to waste them, but I'll try to find a 500 watt online.

You also mentioned office supply transparencies aren't great. I bought transparency film for my inkjet printer, but should I get them printed at Office Depot instead? Or invest in some other type of film? I've seen people double or triple up their printed film, to get an opaque black, but it seems like a waste at $40 per pack of 50.

As for my screen, is it totally ruined? Or would another round of emulsion stripper with a power washer attachment help? I didn't understand how to use the scooper correctly and placed it flush against the screen, instead of using the edge. As you can imagine, the result was a gloopy mess! I'll post a picture, so you can get the full effect. 😅
This is after two rounds of emulsion stripper:
62906DDD-975B-40B7-9E63-3A644F9DA98B.JPG
 

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This is incredibly helpful, thanks!! I have a few more questions for you:

Do 250 watt bulbs not work at all, or are they less effective? I unfortunately had to buy a pack of 250 watts and would hate to waste them, but I'll try to find a 500 watt online.

You also mentioned office supply transparencies aren't great. I bought transparency film for my inkjet printer, but should I get them printed at Office Depot instead? Or invest in some other type of film? I've seen people double or triple up their printed film, to get an opaque black, but it seems like a waste at $40 per pack of 50.

As for my screen, is it totally ruined? Or would another round of emulsion stripper with a power washer attachment help? I didn't understand how to use the scooper correctly and placed it flush against the screen, instead of using the edge. As you can imagine, the result was a gloopy mess! I'll post a picture, so you can get the full effect. 😅
Wattage is only relevant when comparing light sources of the same type, as wattage indicates how much electricity the thing consumes, not how much light, or what type of light, it outputs. A Halogen type light has higher output for a given wattage than a regular incandescent bulb, and it also puts out more UV per watt. The UV output is actually all that matters, as that is the part of the spectrum that emulsion is sensitive to. So, yes, a 250 watt incandescent is near useless (and what I used to burn my first poopy screen 25 years ago). So you want a 500 watt halogen work light. They are portable work lights used by mechanics and in construction and stuff. Usually the enclosure is yellow, always have a glass shield (which you must remove), often have a metal grill/wire shield (which you should also remove. Don't touch the halogen bulb, or if you do, clean it with alcohol before turning it on--else the bulb will crack or shatter. These get very hot. The fixture will have some sort of handle/base combination, which may or may not be of use to you. So to be absolutely clear, do not go buy yourself a 500 watt incandescent screw-in light bulb, as that is not the same thing at all, and wouldn't make much difference. You can buy halogen work lights at Home Depot, or any hardware/tool store, or the like.

Any transparency you can buy at a regular store is pretty weak sauce for use in screen printing. Transparency films made for screen printing can hold more ink, and thus make a more opaque UV blocking print. Google "Fixxons" and/or "Film Direct". Then you'll need to play with your print settings to get enough ink put onto the film. Once you have professional film, you do NOT want to be using the printers default Transparency setting, as that would just print a meager bit of ink. The point of getting the professional film is that you can dump much more ink on it and not make a mess. Say what printer you are using and someone can probably suggest the optimum setting for use with films like those made by Fixxons.

Your screen is very likely quite dead. I still have several of my early failures around as fond reminders ;-) Here's a tip. You can practice coating a screen, over, and over, and over ... no harm done. Just scrape it off and do it again, then rinse out the left over when you are done practicing. The point being just to become familiar with the feel and handling of it. Then just scrape the stuff off and put it back in the bucket. Lower stress than thinking that you have to get this coat perfect or it will kill your screen, yes? Oh, and those yellow "bug" lights they make so insects aren't attracted to your porch light, those work fine as safe lights when working with emulsion.

Have fun.
 

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Discussion Starter · #6 ·
Wattage is only relevant when comparing light sources of the same type, as wattage indicates how much electricity the thing consumes, not how much light, or what type of light, it outputs. A Halogen type light has higher output for a given wattage than a regular incandescent bulb, and it also puts out more UV per watt. The UV output is actually all that matters, as that is the part of the spectrum that emulsion is sensitive to. So, yes, a 250 watt incandescent is near useless (and what I used to burn my first poopy screen 25 years ago). So you want a 500 watt halogen work light. They are portable work lights used by mechanics and in construction and stuff. Usually the enclosure is yellow, always have a glass shield (which you must remove), often have a metal grill/wire shield (which you should also remove. Don't touch the halogen bulb, or if you do, clean it with alcohol before turning it on--else the bulb will crack or shatter. These get very hot. The fixture will have some sort of handle/base combination, which may or may not be of use to you. So to be absolutely clear, do not go buy yourself a 500 watt incandescent screw-in light bulb, as that is not the same thing at all, and wouldn't make much difference. You can buy halogen work lights at Home Depot, or any hardware/tool store, or the like.

Any transparency you can buy at a regular store is pretty weak sauce for use in screen printing. Transparency films made for screen printing can hold more ink, and thus make a more opaque UV blocking print. Google "Fixxons" and/or "Film Direct". Then you'll need to play with your print settings to get enough ink put onto the film. Once you have professional film, you do NOT want to be using the printers default Transparency setting, as that would just print a meager bit of ink. The point of getting the professional film is that you can dump much more ink on it and not make a mess. Say what printer you are using and someone can probably suggest the optimum setting for use with films like those made by Fixxons.

Your screen is very likely quite dead. I still have several of my early failures around as fond reminders ;-) Here's a tip. You can practice coating a screen, over, and over, and over ... no harm done. Just scrape it off and do it again, then rinse out the left over when you are done practicing. The point being just to become familiar with the feel and handling of it. Then just scrape the stuff off and put it back in the bucket. Lower stress than thinking that you have to get this coat perfect or it will kill your screen, yes? Oh, and those yellow "bug" lights they make so insects aren't attracted to your porch light, those work fine as safe lights when working with emulsion.

Have fun.
Thanks for the tips! They've been really helpful in figuring out where I went awry, and I'm on the hunt for a halogen light and proper films. I'm also using an HP Officejet 4632 if anyone has any tips on printer settings.
 

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I'm also using an HP Officejet 4632 if anyone has any tips on printer settings.
Once you've got the right transparency film, you'll probably find that one of the Photo settings works best ... at least I think that is what people use. (I use Accurip, which in retrospect costs a lot for what it is, so I'm not recommending it, but it takes the place of the normal print settings, so I don't have direct experience using them for films.)
 
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