Sensitivity of wet emulsion.

[Maxie]

I think I remember reading or hearing that emulsion is not sensitive to light under it is dry.
is this right?
Can I coat screens in a lit room and dry them in a dark cabinet?

[Dottonedan]

Many try to not answer this questions because there are difference of opinions. The only thing I know for a fact, is that The emulsion Company's will do demo's or video's coating screens in a safe light room. In addition, during one video, they clearly state to coat wet emulsion inside a safe light room as a SOP. That is a Ulano video that can be found on their website. It's a bit dated tho.

It's just a best practice to do so in a safe light room. There are various reasons why some shops can, and others can't. For example, if you do no fine halftones, and your exposure time is compensating for any loss of strength, you can coat in an open regular lit area.

[alan802]

We've coated hundreds of screens under normal shop lighting and I won't go so far as to say it's not sensitive at all but I do know that it's not very sensitive in wet form.  Most every screen I coated during the workshops the last 3 years was done out in the shop and even trying to find a failure due to where we were coating I could not.  Looking at the finer points of developing stencils and under a microscope there was never anything to claim that the emulsions we've used were sensitive in wet form.  Others I'm sure will chime in with differing views but I'd suggest you give it a try and report back with your findings.

[ABuffington]

We ship our emulsion in black buckets to prevent light contamination.  This is a case where it isn't going to kill the emulsion, but it will degrade it.  Leave a bucket out during coating to fluo lights and after several times  it may get lumpy, or not give the details you want.  Does it ruin it?  No  Does it degrade emulsion quality?, yes depending how long it was exposed for.  A question of light strength.  If wet emulsion isn't sensitive try walking out in the sun with an open bucket. (Please don't do this, it will ruin your emulsion).  So typical fluos, probably not an issue, but coating and fine details could be an issue downline after using this method. 

[3Deep]

I coat our screens under 2 4ft regular fluorescent lights, plus I have a single yellow safe light to use when needed,  I think a lot really depends what type of lights and how many you have in your open area that you coat screens in.

[alan802]

I was more answering the question in terms of whether it was safe to coat a screen out in the shop, not so much out in the parking lot at noon on an August day .  If you tried to crawl inside our Richmond Solarbeam with the light on and started coating screens I can see there being problems, but there have been no issues by coating screens under our normal shop lighting.  Give it a try Maxie, I have a hunch that the screens will be fine but you'll never know unless you do it. 

[Screened Gear]

regular lighting in a shop will take a long time to effect the screens wet or dry. Now sunlight will expose it in less then a min. The real question is why are you not just coating in a safe area. Do you like to risk all the work it took to make the screens. Do you want to have issues down the road when you have a hot job. Just find a nice dark place and use a bug light red light or even non daylight LED lights. There is enough variables in this industry why risk anything if you don't have too.

[Maxie]

I am setting up a new plant and am building three rooms, one for screen reclaim, one for drying and one for screen wash out.
The drying room will have climate control and is not really big enough for coating and drying.      I have been printing for 25 years and have always coated in the factory with whatever light there was, mainly fluorescent with a bit of daylight.    I've never had a problem but have also never done any serious testing to see if I could get a better result  coating in a room with the correct lighting.
What I can do is do most of my coating in the factory and if I have screens for high detail work I will have room in the screen wash out room to do this.
Alan you have a room big enough to coat in but you still coat in the factory and as you say you've never had any issues.    I'm sure you are holding fine detail.

[alan802]

99.9% of our screens are coated in a light safe room but a year or so ago this topic came up and many times during the workshops I did we would coat screens out in the shop because we couldn't all fit in the dark room and I never had issues with those screens.  So I did a lot of comparison testing with screens coated in both areas and tried to find something wrong with the screens done under normal shop lights and none of my tools and measuring devices could find anything.

[ABuffington]

As I mentioned it won't kill the emulsion on a coated wet screen, but if SBQ it doesn't take much.  A skylight, an open shipping door, blue sky at a distance may not seem like much but your emulsion would get lumpy if contamination occurred in the bucket, and on screen maybe a little harder to wash out and possible saw tooth edges.  If only fluo shop lamps well above your head no issues, but metal halide hi bay lamps on ceiling still ok for a minute or two?  All depends on how long the screen sits there before getting it into the safe room.