# exposure time question



## superblitz1978 (Mar 11, 2013)

I have a new xvactor exposure unit it says that a 110 mesh should take about 4 minutes to expose. when I took the screen to the washout booth the image wouldn't come out, I ended up blowing out the emulsion in the attempt to get the design out. is this a sign of over exposure or under exposure?


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## dhoffroad (Oct 21, 2010)

could be either, kinda depends on the emulsion your using...


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## superblitz1978 (Mar 11, 2013)

im using the ryonet dual cure rxp emulsion, its the kind you mix diazo with. when I washed it out the water looked really yellow, I guess I under exposed it even though it was in the exposure for 4 minutes?


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## beanie357 (Mar 27, 2011)

Over.
Get an exposure calculator.
Ryonet has em, as every other screen supplier does.
Will save you so much ag.


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## superblitz1978 (Mar 11, 2013)

can you resuse these exposure calculators


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## binkspot (Jun 12, 2013)

Yes, it's a film you can use over and over. It will help you dial in your exposure times. Each mesh count should be tested. 

Major factors in exposure time. 
Mesh count
Mesh color
Type of emulsion
How its coated, 1/1, 2/1, etc
How well it's coated
Film or velum 
Type and wattage of the exposure unit.


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## sben763 (May 17, 2009)

Over exposure or something wrong with the emulsion. I have only used the DXP a few time but never a yellow running off after washing out. Did you mix the diazo with bottled water then mix into the emulsion. 

Also if the screen became in a unsafe light environment at anytime from drying to exposure and before washout it will be over exposed. 

First test your emulsion. Coat a screen, let dry and without exposing washout. The emulsion should come right off. If it doesn't its either bad emulsion or screen was exposed to a unsafe light environment. 

If that works you can do a step wedge test. Coat a screen use som cardboard and move it every 30 sec in. 8 steps. Run a peice or 2 of electrical tape across the entire length of screen. You will have exposure from 30 sec to 4 min. Then washout. Any where the emulsion is soft or washes out is under exposed. Any where it doesn't wash out its over exposed. 

Films can also be an issue but if I remember right you have accurip with all black so it shouldn't be an issue.


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## dhoffroad (Oct 21, 2010)

using that emulsion your under exposed, if your getting "yellow" runoff when you rinse its under exposed, I use that same emulsion and under a 600w metal halide exposure unit I'm at 11 minutes. 

order a exposure calculator, I'd say start at 8 minutes and go from there.....Ryonets RXP which used to be DXP is a good emulsion but it takes longer than others to expose


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## sben763 (May 17, 2009)

I have the same exposure unit and it's only for five minutes with that DXP emulsion.

Ill elaborate more in a bit.


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## dhoffroad (Oct 21, 2010)

oh ok but I still say under exposed if he is getting yellow runoff, when I was under exposing (according to a exposure calc) I'd get that yellow runoff but after I dialed in my times it went away...


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## sben763 (May 17, 2009)

[media]http://www.silkscreeningsupplies.com/files/799934/uploaded/UV%20Exposure%20Unit%20Instructions%202012.pdf[/media]. Per Ryonets instructions. I agree to a point but the OP can't wash out. If you can't washout your not under exposed. Under exposure will washout and blow out easily.

If I remember right you have a home built exposure unit and a nice one! But if memory servers me you have 6500k on the Calvin scale bulb and that usually puts out the red and orange UV spectrum. 500-700nm. If you find a bulb in the 10000k your times for dual cure would be under 2:00 with 600w MH. I have a 1000w I'm building now and I'm at about 45 sec for dual cure and 20 sec for photopolymer. Emulsion exposure is best between 380-430nm depending on type of emulsion. Dual cure likes the higher end 400-430nm and photopolymer 380-400nm. These exposure unit do 420nm. 

I'm gonna guess the OP has a issue before or after exposure and not the actual exposure. Under exposure will ALWAYS wash right out because the emulsion doesn't cross link and there is no bond.


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## dhoffroad (Oct 21, 2010)

Sean thanks for the info, good to know, I've been having a little trouble with my ballast lately its developing a short inside so I've been keeping my eye out for a new one, once I do I'll be able to run a different bulb and would be way happier with a 2is minute burn time....


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## sben763 (May 17, 2009)

[media]http://1000bulbs.com/pdf/plantmax-pxmps100010k-specs.pdf[/media]. Here is bulb I'm using look at the 10k light specs. It peaks at the perfect spectrum. I am using a quantum 1000 watt dimmable ballast. I can run at 50% until I am ready to burn. If you have the setup I am remembering you have a 1000w socket in your reflector. Are you using the glass from you reflector. If so this will cut down on your UV to screen. I just hope mine looks 1/2 as nice as your does.


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## dhoffroad (Oct 21, 2010)

yea I've been looking at those dimmable ballasts. no glass in my reflector that's where I slide my "shutter" in and out....


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## sben763 (May 17, 2009)

That's what I'm looking at doing. I am looking at 1/4 scale RC car servos to automate the shutter. Rearranging shop over the weekend to make room and start the metal frame work. Am I right that you built a metal unit and you do metal fabrication. I do sheet metal work as a HVAC tech but I have only welded a few times although I am told I do a heck of a job on the few projects I have welded. I want to braze or weld a brass nipple into steel. Is this possible or will I have to thread and seal with a liquid metal or silicon. I am using 1" square tube with 45 welded corners For the vacuum lid and want to use it for the vacuum channel and drill holes on inside


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## dhoffroad (Oct 21, 2010)

welding the brass to steel isn't going to work, to do it right what you want is a "weld bung" here is a link to what they look like McMaster-Carr you should be able to get them at your local steel supply place, atleast the ones by me carry them. oh yea there the second thing down in that link...

unfortunately my exposure unit is mostly wood, the only metal on it is the "stand" that is sits on/in...and yea I've been a metal fabricator for over 15 years now.


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## superblitz1978 (Mar 11, 2013)

Well I changed my exposure time and the image is washing out good but the emulsion feels tacky and is running down the screen after I was it out. Its a pain trying to figure this out because I have to do all the washing from my house and printing from my shop because my shop doesn't have plumbing and there's a 30 minute drive back and forth. I was wandering if maybe I didn't mix the emulsion enough?


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## dhoffroad (Oct 21, 2010)

It's possible ? Did you up your time ? You say it's tacky after washout well I'm not sure about that but good indications of under exposure are a slimy feel while your washing out and yellowish color runoff.


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