Originally Posted by Neil Poulsen
Neil, Not quite sure what you mean by primary control...
In the coating process, the need to get the material into the paper in a uniform form is the goal. The amount of solution, method of application, type of paper, soak in, drying time and temp, all effect the coating smoothness, contrast, speed, and quality of the coating.
You can leave your paper in a drying box too long if it is set too high; above 100F. This will cause heat fog as will directly applying heat with a hair drier set too high or used too close.
How long to let it soak in can vary for several reasons. However, thinner papers will require a shorter soak in than thicker papers as a general rule but that can change with sizing, etc. How do you test for soak in time? Coat a sheet, time it, process and observe the print. Best to use one with a good amount to smooth tonal areas in black, mid tones and highlights. Look for grain and paper fiber. A hard part of the process to determine soak in time is that many coating issues can present as if it were related to something else. You may have too much solution, too little, worked it to long, dried it too hot, etc. You should also be test with out any chlorate, or other contrast agent and your normal coating mix ( FO and PT/PD ratio for your standard print). Starting point should be around 1m45s, to 3m.
My drying box is about 3' 3' x 3 1/2' . The heater is located in the back on the bottom. The fan is on the top near the rheostat to insure proper air flow through it to measure air temp in box and not in the heater. The problem with using an external thermostat is that the one located in the unit can prevent it from coming on. I tried it with an old water bed thermostat. It is best to remove the thermostat from the heater but continue to use it.
Why 60% rh for rehumidifacation? It is a good speed point for both PT and PD. PT is faster at low RH and PD is faster at high rH. So if you use a mix ( I start most prints at 50/50) an RH of 60% is a good balance point for speed of your coating. It also happens to allow your paper to lay flat and not be too humid to allow for transfer from paper to negative.
I don't use an air filter on the unit, but I used formica instead of particle board to avoid particle flakes. I don't like particle board due to it's ease of destruction by water or other liquids.
I maintain the RH in my humidifying box with an evaporative unit that I picked up at Graingers many years back. It is nolonger mad but get one that has several speeds, built in reheostat and a wicking action as a opposed to a heated vapors. It also has an additional fan to ensure a good circulation of the air. RH meters can be purchased for $35.
I'll carify more later, need to run