ghostly dags, need help

[DagGirl]

Hello everyone,

 

I need a bit of help in understanding why my images do not appear stronger. I am experimenting with large plates (30X33 cm) and it is difficult to make a nice strong detailed picture. I am using iodine, potassium of bromide, mercury and hypo. it takes a long time to iodise it and just as long to expose it to bromine ( is it possible to expose it for too much?). when I get a nice reddish-orange colour, I insert it into a camera and it takes more then 20 min of exposure to get any results. why so long? is it bad chemicals? bad lens? bad plating?bad polishing? and when I do get a result it is very pale and ghostly like. not to mention that making a picture inside is impossible. no mather how much light I have I do not get any results at all!

 

my first successfully picture was ok, but since then I cant get got results.

I don’t think i am doing anything different. just the scale changed.

 

here are few pics. the firs one was expose for 40 min under the sunlight, the second for 10 min. it was posible to view only for this extreme angle.

 

if anyone has any opinions I would be most grateful

 

thnx

 

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[photolytic]

I admire your courage in jumping into the making of large Dag plates. It is always a challenge, particularly with limited experience in making smaller plates. My advice would be to go back and experiment a bit more with smaller plates.

You have not provided enough information for a diagnosis of the problems you have seen.

A 20 min exposure may be too long or too short, depending upon plate fuming, lens aperture, lighting, or developing conditions.

Developing larger plates requires more mercury and a larger developing apparatus.

More time and higher temperatures may be needed to preheat the box so that the mercury fume concentration is high enough at the surface of the plate. Do you have temperature sensors at the bottom and top of your mercury box?

The plate colors you report could be due to iodine alone or a combination of iodine and bromine.

You mention using potassium bromide, presumably with sulfuric acid, to produce bromine for fuming. Have you checked to see that you have allowed enough time for the bromine fumes to reach the top of your fuming box? My latest bromine measurement of bromine fumes (8/12/08) was .000014 Eq/l or .00112 grams/l of Bromine at the top of the box or approximately twice the molar concentration of iodine fumes at the top of my iodine fuming box at 20C. This is several orders of magnitude less that predicted by the vapor pressure of liquid bromine but still sufficient to fume the plate in 10 seconds.

We hope to hear more of your work in the future.

[drdag]

I made 70 images like that until I ‘got it’ .

Because your plates are so large you will need to have a larger distance between the iodine and the plate to get an even coating. From my failure experiences I would say there is too much Iodine and too much exposure time. I would press on with these images but maybe try Becqueral development, and not using the Bromine or Mercury. Once you have that nailed then move on to the more difficult techniques.

[Jon Lewis]

Photolytic, I’ve never heard of putting a temperature sensor at the top of the mercury pot (not that I’ve heard of much). How does the difference in the temperature of the mercury in the cup versus the temperature at the top of the pot effect plate development?

[photolytic]

Jon,

I first heard of it from Irving.

The top of the mercury box is where the action is.

The mercury fume concentration is proportional to the temperature (and pressure).

If the temp at the level of the plate isn’t high enough, the mercury concentration will be too low and development with take longer. Unless the box is heated or well insulated on the sides as well as the bottom, the mercury evaporated from the cup will condense on the sides before it reaches the plate. If the sides are not heated, the upper portion of the box (and the plate) must be warmed by refluxing the mercury fumes alone, rather like a double boiler in your kitchen.

I develop at room temperature in a vacuum chamber where the concentration of mercury fumes is the same top to bottom, so there is almost no tendency for the mercury fumes to stratify in the chamber

[Jon Lewis]

Thank you, that makes a lot of sense now that you’ve spelled it out. Have you heard of people heating the pot itself and not only the mercury in order to even out the temperature?

[photolytic]

Jon,

Most use mercury boxes made of cast iron or welded stainless steel which conducts heat very well. When the mercury is heated the box is also heated. This eliminates the need to heat the sides of the box, assuming it is well insulated.

Monitoring the temp near the top of the box allows the operator to determine when the box has reached operating temperature. Some add a little heating tape around the sides of the box to help the process along.

[Author]

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