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Today I am too hot and its too humid to put a big effort into the blog.

Just kidding. Well not really, it is very hot and humid here in Rhode Island today.

Nothing like New Orleans or places, but hot enough.

Workers don’t like the heat and the humidity and neither do screens. I did some research and we have some practices in my shop, but I’ll start with some advice from Dave Dellinger from KIWO because I can’t say it any better, although I paraphrase a bit:

?After coating, your screens must be kept dry.

30 to 40% relative humidity is ideal, and never exceed 50%. Too much moisture left in the emulsion and you will have improper exposures and incomplete cross-linking (emulsion curing.) So you will get the following problems as a result of screens that aren’t “dry.”
- Pinholes develop while printing
- Emulsion becomes soft and tack
- Reclaiming becomes more difficult
- Ghost/haze images after reclaiming become more of a problem

Using an hygrometer (fancy name for a thing you buy in a hardware store to measure humidity) is essential. The emulsion can feel dry to the touch, but it is not. Only measuring is accurate.

You can even dry your screens very well in a closet that is heated and vented, or it may have dehumidifiers or any number of great ways to get the humidity out. However, if the storage area (i.e. usually a closet or a stack in the screen room) is humid, the water will go back into the screen and “rehydrate” the emulsion. This is a bad thing and leads to all those nasty problems we mentioned before.

So measure the humidity and if too high, get rid of it. Vented fans are great to get rid of the large amounts of water, for instance from the closet doing the initial drying of your emulsion or from around your sinks.

Beyond that, it is air conditioner or dehumidifier to get rid of moisture. B asic

ally a dehumidifier gets rid of water into a container or a hose and in doing so just sends the hot air back in the room. An air conditioner sends the water outside either dripping or evaporating and sends the hot air outside and the cool air back in.

If it is really humid outside, an air conditioner might have to cool a room down to fifty degrees (brrrrr!) to get rid of enough moisture to bring your humidity down below 50%. Some units even have a reheater to make the room bearable as the AC keeps running. A better balance is probably to have dehumidifiers and AC.

Run the dehumidifiers and when they can’t keep up or it is too hot, put the AC on as well.

And one last piece of advice - make sure the dehumidifier has air flow around it. I’ve seen shops put it in the screen closet in such a way that it is dehumidifying about six inches around it since no air can get to it.
Stay dry.