# emulsion color and exposure times



## skeletrino (Sep 3, 2011)

hello,
i am still pretty new to screen printing, but getting some promising results. 

the question i have is does the color of your emulsion affect the exposure time? i have two different brands of emulsion, cci hybred and ulano. one is reddish pink and the other had a seperate blue dye. the blue emulsion seems to take longer to expose. is this because of the color or just a difference in brands? sort of like white vs yellow mesh? or is the color arbitrary? or possibly does the color relate to what type of printing is being done?

any thanks for any help!


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## tpitman (Jul 30, 2007)

I don't think the shade of color has any bearing on exposure time. The addition of the dye itself I do think increases time, and there are a couple of emulsions that are available as clear, or with the dye packaged separately for you to adjust to your own tastes. I think the reason most come colored is to aid in washout so you can more easily tell how well you've exposed it.
Ulano's Proclaim CL is clear, and I think they make another.


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## skeletrino (Sep 3, 2011)

are some colors better than others with different mesh colors? or is it a matter of personal taste?


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## ZenPrinter (Jul 10, 2010)

The best emulsion I have found after 30 plus years when it comes to speed, accuracy, durabily and PRICE is made by a company called Tubelite. It's called "TTX".

Generally color of the emulsion has nothing to do with exposure. I prefer pink because it is easier to see through but, TTX only comes in blue and I still use it because it delivers everytime; I shoot a lot of halftones.

I shoot with a 5K watt gas halide bulb and my exposure time using clear film on a 230 mesh is 30 seconds. Very easy to use and somewhat forgiving if you under/over expose.


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## skeletrino (Sep 3, 2011)

how does it work with fluorescents? I've been reading that some emulsions won't expose very well with fluorescent units, but that is all i have for now. 

sort of off topic, it does seem that exposures/exposure times seems to be rather rule of thumbish/ experience/ personal taste rather than procedural and very hard to get consistent answers. some of the things i read are all over the place - do this, no do this, etc!


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## skeletrino (Sep 3, 2011)

oops, sorry forgot the whole point of replying!

the cci (pink) w/ fluorescent is running about 1:40 and the ulano (blue) was taking 4:30+ to do the EXACT same screen with clear film. i thought it was possible that the blue was absorbing the uv or something causing the exposure times to be so long. 

also the blue seems to be "thinner" closer to the edges of the detail if that makes any sense. when i hold it up to the light it is pretty consistent in color until you get closer to the edge of the print itself and it becomes more transparent and greenish in hue because it looks like you can see more of the mesh (yellow) through it.


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## ZenPrinter (Jul 10, 2010)

OK I have to get into this one. Exactly what kind of floro bulb are you using?


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## ScreenFoo (Aug 9, 2011)

Not to speak for Zenprinter, but I get the feeling he does not use fluorescents if he has a 5K MH rig. 

What you're describing with the Ulano stencil sounds like poor positive contact--are you using a weight or vacuum?


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## gerryppg (Jan 29, 2010)

skeletrino said:


> oops, sorry forgot the whole point of replying!
> 
> the cci (pink) w/ fluorescent is running about 1:40 and the ulano (blue) was taking 4:30+ to do the EXACT same screen with clear film. i thought it was possible that the blue was absorbing the uv or something causing the exposure times to be so long.
> 
> also the blue seems to be "thinner" closer to the edges of the detail if that makes any sense. when i hold it up to the light it is pretty consistent in color until you get closer to the edge of the print itself and it becomes more transparent and greenish in hue because it looks like you can see more of the mesh (yellow) through it.


 I am wondering which pink CCI you are getting that you are only exposing for 1:40. If its the Diazo version I would think you are underexposing that one. Most diazo emulsions will be in the 5 minute range depending on mesh.


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## ZenPrinter (Jul 10, 2010)

ScreenFoo said:


> Not to speak for Zenprinter, but I get the feeling he does not use fluorescents if he has a 5K MH rig.
> 
> What you're describing with the Ulano stencil sounds like poor positive contact--are you using a weight or vacuum?


I am the one using the 5K MH, Tyson


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## ScreenFoo (Aug 9, 2011)

When I said "he" I meant you. I was guessing that since you had a 5K MH rig, you probably would not have statistics on exposing your emulsion with fluorescents. 

I've been wrong before though.


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## ZenPrinter (Jul 10, 2010)

ScreenFoo said:


> When I said "he" I meant you. I was guessing that since you had a 5K MH rig, you probably would not have statistics on exposing your emulsion with fluorescents.
> 
> I've been wrong before though.


Eh, No Biggy. When I started (too frikin long ago) I used 5500K Photo Bulbs, photo clear glass and the ol' foam and weight bit; then I latched onto an old carbon arc and was lucky enough to convert and old plate vacuum nobody wanted into a vacuum frame. Then I got big and shot 4 screens at a time with a big NuArc 5K MH with light sensors and a huge poly-cop. Then I got divorced. THEN (here it comes) I shot with floro-blacklights to start over. Yeah 3-5 minutes is about right. Ya still can't shoot halftones effectively with that set-up. What I used was a light box 1/ 40 watt light every 6"/ 5" clearance to the photo clear glass. An 1/8" piece of dense foam spray glued to a piece of 1/4" masonite for the backer almost edge to edge to the frame. I put nickles under the corners of the screen used 16 lbs total of bagged sand evenly distributed. Ah the good old days. The only thing I wish I had now was a bigger press. Too old oh well. hehehe


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## ScreenFoo (Aug 9, 2011)

Sweet, now instead of saying "I've been wrong before," I can say "I've been wrong today." (One of my favorite lines  )


As far as the fluo/emulsion situation goes, I'm on the same page--the UV unit I used to use was reasonably quick--two to six minutes for 156-305 screens. Even though halftones get undercut, if you limit your percentages you can work with them.


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## ZenPrinter (Jul 10, 2010)

ScreenFoo said:


> Sweet, now instead of saying "I've been wrong before," I can say "I've been wrong today." (One of my favorite lines  )
> 
> 
> As far as the fluo/emulsion situation goes, I'm on the same page--the UV unit I used to use was reasonably quick--two to six minutes for 156-305 screens. Even though halftones get undercut, if you limit your percentages you can work with them.


I hear that. Since I got into this thread I have been thinking about those 1/2tones. There has to be a way. I am thinking that those chrome coated 1/2" grids they use in office lights might straighten out the light deflection to stop or at least lessen all those Hz bouncing around. Hmm how far between the light source and the glass is one of the questions.

One thing I forgot to mention is that the matt behind the screen (the foam in this case) has to be black.

So where can I go on here to get a real employee?


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## ScreenFoo (Aug 9, 2011)

I was debating the same thing although I was thinking a flat black grid would do a better job killing the improperly aligned light, but more than a couple times, I've been looking up at that style of fluo fixture... scratching my head.
As much as it sounds like sacrilege, I would switch to a quartz over a fluo setup--they're both crappy light sources, might as well have a crappy point source instead of a crappy diffuse one. Oh wait, I did. 


I know it sounds sad, but I'm starting to think it isn't worth trying to train. Seems like everyone is the greatest worker in the world when they want to get their foot in the door, but the initiative vanishes shortly thereafter...


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## skeletrino (Sep 3, 2011)

i have a 24x20 box, simple aluminum box. since im just getting started, i didnt want to learn to drive in a race car! it has 8 bulbs, not sure which brand. came from ryonet. i sense alot of eye rolling here, but it seems to get the job done.

i wondered about under exposing, because when i wash out, a little pink comes off the back, but the stencil looks clean and crisp and seem to be better off than the ulano. and on a step test it washes out to a 7. 

what i do is this: i place my film on the on the screen, put it on the light box with a foam insert, then i use 4 pieces of plate [email protected] about 20lbs each to distribute the weight. i get good screen contact (i think) because the stencil looks pretty crisp.

but this leads to another question. once the screen has been exposed, can it be re-exposed? say it is under exposed, but you wash and throw it on the lightbox again to finish exposing it? does that work?


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## ScreenFoo (Aug 9, 2011)

Yes and no--if you're using a diazo or dual cure, (like the cci stuff) and the color hasn't changed completely (i.e. it's still "yellow") you can dry the developed screen and put it in the sun for a little while. 

I do it with the idea that uncured emulsion is weaker and hard to reclaim, but doing this with an underexposed screen doesn't seem to change a lot... YMMV.

Speaking of, what kind of emulsion is the Ulano that you're using?


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## ZenPrinter (Jul 10, 2010)

OK we are moving now. Black might work as UV is outside that spectrum. Good idea. Is there such a thing as reflective black? fffffffff I don't know. WAFTP (WOW A F THINKING PERSON) Rock on!

If I didn't live in a nice country house I'd work with you. I just want to go out with a bang and leave my shop to the employees when I finally get to enjoy fishing, bbq, beer and a cell phone to advise them (on Wednesdays only). hehehehe


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## skeletrino (Sep 3, 2011)

on the subject of straightening light out from floros, wondering if anybody tried polarizing film like off of lcd tv? possibly the loss would be outweighed by gains in uniform lighting?


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## ScreenFoo (Aug 9, 2011)

I'm not too up on the physics of polarizing light, but I don't believe a filter actually "straightens out" the *path* the light travels--anyone teaching applied physics classes? 

Oh, and I'd think that flat black would be preferable to gloss, no specular reflection?


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