[trailheadgirl]

Hey everyone,

I've been having trouble with washing out the emulsion after exposure to a halftone image. I am using Chromaline ChromaBlue emulsion, one coat of both sides of the screen, I let the screen dry overnight, and expose it for 2 minutes to the halftone image. I have done a step wedge test - my original one in the summer said the ideal time was 90 seconds, but this one I did a few days ago (trying to trouble shoot my problem) seemed to indicate that 2 minutes was better. The step wedge test washed out fine, too, as does any other image that we have burned lately. Just these halftones seem to result in the emulsion peeling off of the screen. I made sure that the screens are cleaned thoroughly before they get emulsion. They are left completely dark, overnight, and I wash them out after exposure with a pressure washer. The first image was with a garden hose that I could control the pressure and spray of.

Any suggestions would be helpful. I originally thought the coldness of the drying room and the water we use to wash them out was the problem, but I've since added a small heater in the room to keep it about 65-70 degrees, and I added some hot water to the cold water so it is about lukewarm to mildly cold now. I have also had this problem with two different batches of the same brand of emulsion. I've used this emulsion for at least 6 months now with no other issues, including doing halftone images. I'm out of ideas at this point.

Pictures, the first one is with the garden hose, the second one is with the pressure washer: https://imgur.com/a/rOI6m

 

[Frienzy]

If this emulsion is pure photopolymer (without diazo added in it) you might need to add diazo to use it for halftones.
But from pics it looks waaay underexposed.

 

[trailheadgirl]

It's not a diazo emulsion, why would adding diazo to it help with halftone images?

A lot of people are saying it's underexposed. 90 seconds is my usual time, but I upped this to 2.5 minutes, after doing a step wedge test 2 days ago. I'm doing another step wedge today, to double-verify what time will work best. But I'm worried that anything above 2.5 minutes will be overexposed, because these dots are so tiny, that they will be very hard or nearly impossible to wash out if I expose them to too much light.

 

[rcrotty82]

What mesh count? Did you use hose or pressure washer? It looks like WAY too much water was used trying to clear the screen and you saturated the emulsion to the point it broke down.

 

[trailheadgirl]

Mesh count is 305, since we are trying to wash out a halftone image. I've used both a hose and a pressure washer at this point, both of them resulted in the same effect on the emulsion. I just did a step wedge test now, and the whole thing washed out, from 30 seconds to 5 minutes. So I'm baffled at this point.

I thought maybe it was too much water being used with the hose, which is why I switched to the pressure washer, to make the process faster. But it starts to peel like the pictures immediately, as soon as any of it starts to wash away. I think the emulsion must not be adhering to the mesh for some reason, either the humidity, or underexposure, or perhaps the cleaning process leaves the screens greasy, though I can't see how since I do it myself. I've switched from Dawn dish soap to Ajax, which I hear is a better degreaser, and I bought a brand new brush, to hopefully rull that out. It's just a process of elimination at this point.

 

[rcrotty82]

You mentioned you have used this same bucket of emulsion on other screens with no issues correct? I assume those were also de-greased that same way as the 305? I have never used dish soap as a degreaser so I really can't say if that is or is not an issue, maybe try some simple green? Do you run a dehumidifier?

 

[trailheadgirl]

Yes, I've used this same bucket, and other buckets of the same emulsion, with no problems. Everything has been cleaned and degreased in the same way for years now. I do use a dehumidifier. Simple green is an interesting idea, I might try that. Is it a good degreaser? I'm thinking at this point that the problem has to be underexposure or an improperly cleaned screen. Can't think of anything else it could be.

 

[Twisted Grafix]

What kind of exposure unit do you have? Is the bulb(s) going bad?

 

[trailheadgirl]

Funny you mention that, I checked the table out yesterday, thinking this same thing. It's a Lawson ExpoLight, and there were 2 bulbs that were out, right in the center of it! I moved them to the edges and moved two of the working ones to the center, and tried burning my image again yesterday - same problem. Also tried the step wedge test this morning, and blew the whole thing out. So I fixed a problem, but apparently not the one that is causing my issue.

 

[Twisted Grafix]

All the bulbs have to be in working order to get enough fully saturated light and a nice, even light coverage over the emulsion to properly crosslink it. The other thought is that the bulbs are on their way out so the wavelength may be less than ideal. Keep in mind that the bulbs may look like UV light, but the wavelength is what really matters when exposing. Brightness doesn't matter much as long as the wavelength is saturated in the proper range.

 

[trailheadgirl]

This is an interesting idea. The light table is old, so this might be the problem. How do I check the wavelength of the bulbs?

 

[Twisted Grafix]

This may be a little long-winded....

In my research, you would have to use a spectrometer with a diffraction grater film to break down the visible (red, orange, yellow, blue, violet) light colors. The wavelength is measured in nanometers (nm) and each light color or energy is in a different wavelength range. Microwave, x-ray, infrared, gamma, and TV/radio are not of any use, thus no concern to us now. Ultraviolet light is mainly non-visible, however, it does have a small section in the violet range. This is the range (about 320nm-410nm) that the exposure units are based off of. The lower the nm rating, the higher the energy output. Think of it this way, if a 100w bug light bulb is installed in your dark room, it will give off a yellow light (590nm-565nm), but the emulsion will not expose because the wavelength is in the wrong spectrum. If an unfiltered UV blacklight is installed (450NM-320nm), the lighter colors in the room will glow, but the room will remain fairly dark. Your emulsion will have a better chance of exposing due to the intense UV energy given off in the proper nm range.
You could easily test this without spending a penny on expensive spectrometer testing equipment. Take the screen outside and utilize the sun. The sun produces all sepctrum of wavelengths. (similar to the thought process of a metal hallide multi-spectrum unit). Using the sun will allow all spectrums to cross link the emulsion. If it exposes properly, then you know it's the bulbs. If it doesn't expose, it's bad emulsion. Another way is to replace all the bulbs and do another test in the exposure unit.
Older bulbs will shift out of the needed range over time and will have to be replaced. It doesn't matter is it's halogen, fluorescent tube, CFL, or metal hallide.

Hope this helps!

 

[trailheadgirl]

Thanks so much, this is great advice. I'll try this next Tuesday and see if it works (it's cloudy and rainy here now). I have tried everything else, and I had no idea the bulbs could go bad, so hopefully this is the answer!

Cheers and merry xmas!

 

[NoXid]

Twisted Grafix nailed it. Emulsion expires and bulbs burn out. Check the emulsion and replace the bulbs.

 

[Twisted Grafix]

Please let me know what you find...

Merry Christmas!

 

[sben763]

Thanks so much, this is great advice. I'll try this next Tuesday and see if it works (it's cloudy and rainy here now). I have tried everything else, and I had no idea the bulbs could go bad, so hopefully this is the answer!

Cheers and merry xmas!

Unless the chroma blue has the manufacturing date of 1 year or longer are was exposed repeatedly to a uv source it’s likely not the emulsion.

The older Lawson expo lights were supplied with 2 different lights and are interchangeable. The can have daylight or unfiltered black lights. The unfiltered blacklights will need to be ordered while most big box hardware stores carry the daylight bulbs. The unfiltered black lights put out 2-3x the uv of a daylight.

Fluorescent lights age as they have mercury gas as well as a few other metals depending on the bulb and purpose. They can leak as well as the metals will deteriorate with use. They should be changed at least every 2 years with light use and every year with heavier use.

Another thing is humidity. If it’s moist when exposed the sensitizers are not as sensitive. I have a dehumifer in screen room to keep the variables consistent.

Also with colder weather fluorescent bulbs may need a 2-3 min warm up period before exposing. If you have ever had fluorescent lighting and in the colder months notice they are dim when turned on and 2-3 min later that are much brighter. This is due to the gas being much more condensed.

 

[trailheadgirl]

Sun exposure was inconclusive. I think I exposed it too much, barely any of it washed out.

On the plus side, I used my regular light table and did some exposures, and they are better than the ones last week. I think my problem might have been humidity in combination with an extra thick layer of emulsion on some screens. I put two thin layers on screens, let them sit 4 days, and they washed out without that strange effect this morning. The negative is that I still have trouble getting the tiny details out without washing away some of the other details. Working on fixing that now. Halftones are frustrating

 

[trailheadgirl]

Unless the chroma blue has the manufacturing date of 1 year or longer are was exposed repeatedly to a uv source it’s likely not the emulsion.

The older Lawson expo lights were supplied with 2 different lights and are interchangeable. The can have daylight or unfiltered black lights. The unfiltered blacklights will need to be ordered while most big box hardware stores carry the daylight bulbs. The unfiltered black lights put out 2-3x the uv of a daylight.

Fluorescent lights age as they have mercury gas as well as a few other metals depending on the bulb and purpose. They can leak as well as the metals will deteriorate with use. They should be changed at least every 2 years with light use and every year with heavier use.

Another thing is humidity. If it’s moist when exposed the sensitizers are not as sensitive. I have a dehumifer in screen room to keep the variables consistent.

Also with colder weather fluorescent bulbs may need a 2-3 min warm up period before exposing. If you have ever had fluorescent lighting and in the colder months notice they are dim when turned on and 2-3 min later that are much brighter. This is due to the gas being much more condensed.

I agree that it wasn't the emulsion, especially considering I did this with both an older emulsion and a brand new gallon. I think you're right it must have been the humidity, even though I had the humidifier going. I also think that the thickness of the emulsion on the screen might have played a part, leaving the back side of it underexposed so that it didn't adhere to the screen.

Do you know how I can figure out if I have fluorescent light bulbs or UV black lights? My boss is insisting that we have UV lights, but I think they might be fluorescents. And they are probably at least 5 or 6 years old, I'm guessing closer to 10 years old.

 

[sben763]

I agree that it wasn't the emulsion, especially considering I did this with both an older emulsion and a brand new gallon. I think you're right it must have been the humidity, even though I had the humidifier going. I also think that the thickness of the emulsion on the screen might have played a part, leaving the back side of it underexposed so that it didn't adhere to the screen.

Do you know how I can figure out if I have fluorescent light bulbs or UV black lights? My boss is insisting that we have UV lights, but I think they might be fluorescents. And they are probably at least 5 or 6 years old, I'm guessing closer to 10 years old.

The bulb is marked on the end. BL will usually start the part number for black lights. FL for standard. After initial bulb use after 2 years there is 50% or less UV from the bulbs. If they are that old they are putting out less then 25% UV.

If you get new bulbs time will shorten but more importantly it will cook(expose) the screen fully.

 

[Industryps]

Other user have offered some great tips for your consideration, but let me offer one more idea that has yet to be brought up...

What are you using for your film positives? With halftone images, you need to make sure that black parts of your film are REALLY OPAQUE... this is especially true for small halftones and when burning on a 305.
Is the film for your step test a different type of print than your film?

In our experience, a 305 burns considerably faster than other dyed mesh counts. On average, our 305's burn in roughly half the time of a 156 and still faster than a 230.