Platinum Sun Exposure and Split Back Frame
While figuring out how to get some bl bulbs together in my part of the world, it occurred to me that maybe using the sun wouldn't be so unreliable if you just use a split-back frame. I'm guessing this is how it was done back in the day, of course. Once you get a feel for how a well exposed print looks, it shouldn't be too hard to repeat, sort of like DBI. So I'm curious what kinds of problems people have had when trying this approacj (I live in a very sunny area, even in winter, btw).
Also, are 2 18W BL bulbs enough to expose an 8x10 platinum print, or do I need more power? And finally, does platinum paper fog over time? Someone is sending me some old Palladio paper, and I wanted to know if it's worth it. Thanks,
You certainly can use the sun in a split-back printing frame.
The conventional Pt/Pd techniques are developing out processes - that means that the latent image after the paper is exposes is almost invisible, and you really can't see much until you put the paper into the developer. The traditional wisdom is that a print is properly exposed when you see a hint of the final image, but I have never figured out exactly what a "hint" is.
You might want to look into the ziatype process. That is also a Pt/Pd process, but it is a printing-out process - the image forms directly during exposure, and the chemical step is primarily a fixing step. Ziatype would seem to be a natural for use with the sun.
As to the number of bulbs you need - ideally, the bulbs should be 4-6 inches away from the paper during exposure. And of course you need enough bulbs to be able to get even illumination across the size print you are making. If you attempt to get by with fewer bulbs, and increase the paper to bulb distance to even out illumination, your exposure time will increase greatly.
If you are using black-light tubes, it may be possible to make 4x5 inch prints with only two tubes. I would be concerned that if you align the bulbs close enough to the paper to get reasonably short exposures on 8x10 prints, the illumination will be uneven.
You really need four BL tubes to adequately cover 8x10, but you can squeak by in a dire pinch with three. The risk with using the sun as an exposure medium is that the paper will get too hot while exposing. As pt/pd paper dries, the exposure time begins to shift, and image quality will degrade. You can guesstimate your exposure time if you leave some sloppy border outside the negative area because you can watch the color/density shift of the borders. When your borders are a uniform dark gray/gunmetal color, you're good to go, regardless of how much ghost image you do or don't have under the neg. If you over expose, you'll see the borders revert to this grainy blotchy texture, instead of being uniform. Depending on where you live, what time of day you try to print, and the weather, this exposure time could be anywhere from a minute to an hour. If your exposure times are too short (under 3 mins) it is hard to adjust the print if you look at it and say, "That needs to be a half-stop darker". Also, with too fast printing times, your margin between a half stop darker and overcooked could be too short for you to accurately control.
If you've got the old palladio paper, it would be worth a try, but I would first humidify it before printing. Get a large tray, fill it with steaming water, and pass the paper over the tray until it gets limp to the touch. To make sure this humidification gets into the core of the paper, you may need to do this several times. You can do this in subdued room light. When your paper is nice and humidified, print with it immediately. Depending on how old the paper is and its prior storage conditions, it may well be fogged. But then again, folks are printing on Azo made in the 1930s successfully, so this may work as well.
The paper might get too hot in the sun?!! I have done a lot of sun printing and I don't notice the paper warming up much at all. Maybe because it isn't generally that hot in Oregon. I also have a printing station set up with four! 275 watt UV curing lamps. The print can get much hotter than in the sun, yet I have had no fogging problems.
When I print in the sun I make sure to set the print facing square to the sun. I guess that is obvious. Also the color of the black can turn different shades in the exposure from the same print depending on the amount of moisture left in the paper. Plus judging by the black border would assume a very consistant negative density in your production.
Fluorescent tubes produce an amazingly diffuse light pattern. Placement of the UV tubes 4-6 inches from the printing frame was proven unnecessary by Judy Siegel. In one issue, I believe the ninth, of the Post Factory Journal, she did a test which showed that regardless of this distance banding is not evident. For the final part of the test she blacked out every other bulb and laid the paper directly on the tubes - there was still no banding evident.
Two tubes will work, but printing times may be excessively long. Since there is now a 100 watt screw-in fluorescent tube available, the most economical method of building a UV box for 8x10 is the use of one of these. The ballast is built in thus reducing wiring and cost. Printing times should be reasonable.
As for Pt/Pd edges reversing (solarizing) with long exposures, I have never seen this with the combination. It is not uncommon when printing Pd alone. If such prints are developed in potassium oxalate the solarization is often visible in shadow areas.
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Is that a regular or bl screw in 100w bulb? If regular works at that wattage, then that's easy. Otherwise, where do you get the bl screw in? Also, is that actually 100w, or equivalent to an incandescent 100w?
It is listed as 100 watt in the same listing which lists 18 watt. So I believe it is 100 watt.
Check the listing on the bulbman site.
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BLACK LIGHT URBAN MYTHS AND OTHER BLAHBLOGERY
YOUR POST IS A BREATH OF FRESH AIR RE THE IDIOTIC USE OF 20+ BL LINEAR BULBS IN OVER PRICED AND BRUTE FORCE OVER ENGINEERED 200 POUND "UV EXPOSURE UNITS"
Originally Posted by Jim Noel
i guess it's time for " those who know to tell those who don't"
there are a multitude of uv cfl screw base self ballasted bulbs in 100+ watt BUT YOU WILL PAY $40 + FOR IT
i use the uv led screw base units myself-no heat and 8 min exp time at 6" on blueprint paper-a single 28 led screw base will cover 4x5 at that distance-at 12" you get 8x10 cover and 15-20 min exp
a properly designed linear unit of approx 3x4 ft wil only need 4 20 watt bl bulbs to give good coverage and reasonable times
i used to custom build them but that was for commercial shops who had to make a living for their employees, so they knew what they needed and were'nt guessing
vaya con dios
Where do you get the led screw base UV units, and do you use just one 28 led? I'm not in the States, so the KIND of store, rather than a company's name, might be more useful. Electronics stores rather than a Home depot type place? Thanks,
Can you post a link to an example? I may have to build a new light box, but if you can make my life easier then I'll be forever grateful
Originally Posted by z-man