Originally Posted by Neil Poulsen
Neil, A lot of the drying techniques and methods used depends on personal preferences. As Kerik stated, different papers will require different absolute times. For many years, I dried with a hair dryer for 1 to 2 minutes on the front or coated side, then flipped it over and dried the backside an additional 4 to 6 minutes depending on paper. For the last 8 years, I have been coating and placing directly into my drying box for a required length of time. Directly here means after the paper has properly sat and soaked in the coating. The box is kept to 100F with a small ceramic heater and the air is cirulated with an additional 5 in pancake fan. The dials have been removed from teh heater and relocated in the box to keep the readings based on air temp and NOT that of the heater and it's elements.
After drying I rehumidify my paper for 1/2 hour to an RH of 60%.
The key to drying is to not dry to hot and begin at the right time.
It sounds like your primary control is the amount of time you let the paper sit prior to placing it in the dryer. Or, do you find that you can leave it in the dryer too long?
How long do you let it sit for Crane's patinotype, the offwhite variety? Bergger Cott 320?
What's the placement of your pancake fan within the dryer and with respect to the heater?
Placing the thermostat inside the heater is a good idea. In building my warming bath, I found a thermostat at a Jacuzzi repair shop that controls to just over 110 degrees, and which connects to 120 volt circuits. I could use this device to moderate the heating, plugging the heater into a plug connected to this thermostat. It's adjustable. I think this thermostat was just under $30.
Why did you pick 60% r.h.? (Just curious.) I'm wondering if I can find something that's not too expensive that will maintain a particular relative humidity in my small darkroom? I've been looking for some kind of r.h. meter that I can put on the wall, but haven't found one. Or, have a humidifying chamber of some sort.
Do you use any kind of a filter? My ceramic heater has a filter on the back. I wonder if this would be enough.
Thanks for your response. I don't think this kind of heater would be that difficult to build. I'm a master, when it comes to particle board! Heavy, but it does the job.
Originally Posted by Kerik
Thanks for your comment. What effect does the amount of sit time have on the paper or printing characteristics. How do different times affect the image visually?
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