Real Talk: Emulsion Problems
When your emulsion is acting up you need help fast. If you don't have time to read all of this, assume your emulsion is under-exposed. That's right! I went there. If you do have time to read this, I am going to discuss some common and not so common emulsion problems. I may even add photos as I am really working hard these days. Well, that and I realized that cell phones take pretty decent pics and they can often tell a story. Who knew?
Before jumping into the problems, you know I have to ask...how are you testing exposure time? Please tell me you aren't rubbing white paper towels over top of it looking for color transfer. That is soooooooo old school. How about we get you a 21 Step Sensitivity Guide? It's not high-tech. It's not sexy. It is pretty darn effective though. Not so good at math? It's ok, my cell phone also has a calculator. Technology, right? E-mail me a photo of your rinsed out 21 Step Sensitivity Guide and how long you exposed the emulsion for. I will work it out and even show you how I did the math. My seventh grade algebra teacher will be so thrilled as I never did this for her class. Do one thing for me though, rinse the test image area pretty hard. Don't hold back. This will give you an accurate result to work with.
Pictured above is my famous 21 Step Sensitivity Guide. Each rectangle is a gradually darker/denser tone of black. The darker the rectangle, the easier it will be to rinse out after you expose the image. The goal is to rinse out this image and be left with #2 through #7 still in the screen. #8 and below should rinse out. If that happens and you rinsed hard, you will be free of over and under-exposure problems. If not, the back of the envelope provides instructions to increase or decrease exposure time depending on your result.
Alright, on with it already! Here are the most common emulsion problems and causes:
Little dots of missing emulsion. This is a frustrating little problem as you may ruin numerous prints before noticing the problem. Luckily, this is an easy problem to stop in its tracks. First, clean your exposure glass. Sprayway Glass Cleaner is pretty awesome stuff if you want the best. Regardless, any speck of anything on that glass will expose into the emulsion. Second, check your film positives for any stray dots. This can happen with both inkjet and laser printers. If those two options don't change anything, you have a screen prep problem. Degrease the screen and be sure to rinse with plenty of water. Keep in mind a pressure washer does not use as much water as it appears. A regular hose would be great to flood the screen. If you are not degreasing your screen, you simply will always be riddled with pinholes among other problems.
One alternative answer could be contamination in your emulsion bucket. Perhaps you were coating a screen which was not clean. The contamination from this screen made it into your scoop coater. You poured the excess emulsion back into the bucket. Now you have a bucket of emulsion with built-in pinholes. Not good.
Yet another possibility is old emulsion. I would only consider this if there are pinholes almost everywhere. A diazo or dual-cure emulsion has about 8 weeks of shelf life once it is mixed. When it goes bad, you may see a screen riddled with pinholes or it may simply not expose.
Residue in Image Area
If you are fortunate, this is just a sign that you need to rinse the image area out better. If you are less fortunate, this is due to under-exposed screens. If that is the case, reclaim this screen i