[Pobboravsky]

What f/stop was used on the lens?

Subject to lens distance?

EV (exposure value) measurement using a light meter?

Irv

[Pobboravsky]

Jason, I’ve seen crappy pictures but yours don’t even approach crappy. I know crappy from my own experience.

Irv

[Pobboravsky]

Avoiding the use of metal in sensitizer design

My sensi-boxes avoid using any springs by having a wood disk in the middle of the box floor. The disk is about 0.25 inch thick with a diameter of roughly 1-1/4 inch. The top edges of the disk are rounded. The Pyrex dish sits on this disk.

The cross bar has two wood screws instead of one. They are located near the outer parts of the cross bar. Think of the disk as the fulcrum of a teeter totter and the wood screws are where the kids sit at each end of the bar. The craftsman who built the boxes thought of the design in response to my request to avoid any exposed metal.

The boxes have worked well for nearly 40 years. Hard to believe I’m only 39.

Irv

[Pobboravsky]

I don’t know the exact mechanism for Becquerel Development but my best guess appeared in Study of Iodized Daguerreotype Plates published in 1971, p.40.

[/quote]Unexposed silver iodide is normally insensitive to red or yellow light. However exposure in the camera produces latent-image silver specks large enough to act as optical sensitizers so that yellow or red light can selectively photolyze the exposed crystals, leaving the unexposed crystals unchanged. The image consists of finely divided, powdery silver instead of the mercury-silver amalgam found in conventional daguerreotypes. …

Quote:

What is optical or dye sensitization?

Photo-sensitivity to green, yellow and red light is produced in silver halide crystals by coating the crystals with a dye, or dyes that absorb light of these colors.

All silver halide (AgI and AgBr) photographic processes inherently absorb only UV radiation and blue light and therefore are only sensitive to ultraviolet radiation and blue light. This is because they do not absorb green, yellow and red light. If these colors are not absorbed they cannot produce a photochemical reaction; in other words they cannot produce a latent image. Manufacturers extend the color sensitivity of films into the green, yellow and red by adsorbing one or more dyes onto the surface of the silver halide crystal. The dyes absorb green, yellow and red light and transfer the absorbed energy to the silver halide crystal.

When an iodized daguerreotype plate is exposed to an image in the camera a latent image is produced consisting of a small cluster of metallic silver atoms, a so-called silver speck on the surface of the silver iodide crystal. The number of silver atoms in the speck is roughly proportional to the intensity of UV/blue light striking that silver iodide crystal. The highlights receiving the highest intensity have the largest silver specks and the speck size decreases to zero for those silver halide crystals receiving no exposure; that is, the extreme shadows.

My best guess for the mechanism of Becquerel-development is that the silver specks produced by the camera exposure can now absorb light in the green, yellow and red parts of the spectrum. It is as if the silver iodide surface has been dye sensitized image-wise by the camera exposure. Exposing the plate to a uniform red light during Becq-dev’ment reduces to silver only those silver iodide crystals that have latent image specks of silver. In other words, only those that have the Mark of Zorro are zapped.

[Pobboravsky]

Andy,

My test was done with the LEDs 10-inches from the plate. The EV was 6.7 as measured with an incident meter (ISO set at 100). Very similar to Photolytic’s readings.

Is there a hotspot for each LED on the illuminated surface? It is of course a concern but the only question I was asking of the test was: Would it even work for BD? As you pointed out illumination uniformity across the plate surface could be affected by the design of the LED.

Phuphuphnik said:

Quote:

The other thing to worry about is any pattern the die may leave. By this I mean the lens on the LED might focus the shape of the emitter. To get by this you can scuff the lens to make it diffuse.

.

The light can be diffused in a number of ways (opal glass,for one.)

[Pobboravsky]

The 20 mA of the high-intensity red LED in phuphuphnik’s link is 36 times the power of the 0.55 mA of the LED I used in my cheapo test. I would imagine that a square array of the 20mA LEDs would reduce Becq-Dev’ment time by a lot.

(Phuphuphnik: love that that name; it is so-o-o melodious)

A hearty dark bread could be called Phuphuphnikel. I’d best take 2 aspirins and lie down and hope I’m better in the morning.

[Pobboravsky]

Feasibility of Red LEDs for Becquerel Development (BD)

I was so intrigued by the possible advantages of using red LEDs for BD that I bought a PAR38 168 LED Grow Light BUDDING LOWERING FRUITING, red , (It cost $30 + $5 shipping.) It has 168 red LEDs in a circular array and runs at 120 volts, 11 watts.

This is 92mA for all 168 LEDs; 0.55mA for each LED. This is definitely not a high-intensity LED.

There are higher intensity red LEDs but they cost more and my aim was limited to seeing if it would work at all for BD. If it worked with this 11-watt array, development time would be shorter for higher wattage units. The diameter of the circular array was 12cm (4.7 inches) limiting the plate size to 3.25 x 4.25 inches.

Result: These low-intensity red LEDs did work for BD. However, a tungsten bulb + Rubylith are easier to implement and also cost less.

---

Here are some of the observations from the preliminary exposure-development test on an iodized plate. By shifting the dark slide, subsequent thirds of the plate were given 5, 10, 15 minutes exposures. These exposures correspond to 20, 40 and 60 times what is needed to expose an I-Br-mercury-developed plate.

• After 3 minutes BD a faint image was visible when viewed at an oblique angle. However, no image was seen when the plate was viewed at 90 degrees, just a very hazy opaque appearance.

• Development was stopped after two hours. The developed image looked strong and brownish in hue.

• After hypoing for 2 minutes, rinsing and drying the image weakened considerably and the hue shifted to blue. The plate was not gilded.

• There was zero fog in the shadows; the LEDs were just slightly warmer than room temperature.

• The 15 minute camera exposure gave the strongest image. This corresponds to 60 times what would be needed for an I-Br-Hg plate. This is an ISO speed of 0.00083; this agrees with the ISO speed published in Study of Iodized Daguerreotype Plates.

• The illumination intensity of the circular LED-array seems to be greater in the center of the field, but that is uncertain. A square array of say 10-inches on a side would yield a more even intensity while covering larger plates.

I wonder if image weakening in the hypo stage can be minimized by boiling the water used to prepare the hypo solution. Boiling drives off dissolved gases. After allowing it to cool to room temperature add 15g sodium sulfite. After that is dissolved add 15g sodium thiosulfate to make a liter of solution. Decrease hypoing time to a minute.

The major advantages of BD with high-intensity LEDs are: 1. Much shorter development times, and 2. little or no fog depending upon how warm high-intensity LEDs turn out to be.

[Pobboravsky]

RED LED panel, ~12 x12 inches, 225 LEDs $41.00 free shipping.

Product Features

* Body material: Thermoplastic

* Circuitry board material: Diecast Chrome Color: RED

* 225 RED light LEDs: 650nm (nanometer) wave length

* Working Voltage: 12V or 110V-220V

* Power: 13.8 Watts Dimensions: 12 ¼ inches (30.5cm) square

Product Details

* Shipping Weight: 2.3 pounds

I wonder if this will work for Becq-dev?

12volts – wonder if it can be powered by cigarette lighter in car?

Almost seems too good to be true.

[Pobboravsky]

Andy: I know of no published data on the most efficient wavelengths for Becq-dev. However I am reasonably certain that a wide band of wavelengths (say, from 550-700nm) will work. I used a transparent yellow plexiglas panel and a tungsten lamp for Becq.-dev. See Figure 21, p.41 of Study of Iodized Daguerreotype Plates.

Reading the Wikipedia entry on LEDs makes me believe that using a bank of LEDs for Becq. Dev has a high probability of success. http://en.wikipedia.org/wiki/Light-emitting_diode

Some interesting tidbits:

Quote:

The development of LED technology has caused efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s. It is called Haitz’s Law.

– there are LEDs that emit both red and green light (which looks yellow). I think that would be good for Becq.

– there are computer monitors that use R,G,B LEDs instead of a fluorescent tube + filters. I think that it would possible to display a yellow screen (R+G LEDs on — Blue LED off) to see its Becq-dev possibilities.

– there are organic LEDs (OLEDs) on flat panel TV sets that are said to produce spectacular images (I’m assuming here that spectacular means high brightness)

[Pobboravsky]

Just learned that LEDs come assembled in flexible and rigid strips.

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Flight_bars-rigid.html

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Flight_bars-flexible.html

[Pobboravsky]

At first I thought an amber (or yellow) LED would cut Becq-dev time compared with a red array. I was wrong. I assumed incorrectly that the amber LED would be emitting both red and green light. It actually emits yellow/amber light centered on ~590nm. (Similar to a low-pressure sodium light.)

It may very well be that either a green or red LED could be equally effective at Becq-Dev. Or even a yellow/amber LED. Depends upon the available effective intensities. By effective I mean the development response of the daguerreotype plate.

[Pobboravsky]

Andy,

Your light-tight box could be the plate holder which held the plate during exposure. To satisfy the plate-peeking urge put the darkslide back into the holder. cover the holder with ruby/amberlith and withdraw the darkslide. A very small box would enclose the holder + LED array. The rogues gallery list identifies some high output orange and red LEDs. (Or if you want to practice your mountain climbing skills you could shimmy up a traffic light pole and use the traffic light red LED array — yes, my silly gene just kicked in)

[Pobboravsky]

Rogues gallery of LEDs: http://www.oksolar.com/led/led_color_chart.htm

[Pobboravsky]

Re: Becq. dev’ment, heat, long dev’ment times

I wonder if a 2-dimensional array of tightly-spaced red LED’s would overcome some of shortcomings of using a tungsten light source for Becq. Dev’ment. LEDs give off very little heat so a fan would not be needed. Rubylith would also not be needed. And I wonder if dev’ment time might be reduced if the array was spaced ca. 1/2 to 1 inch away from the plate. Hours long use of a tungsten lamp + fan eats up a lot of electrical energy and is very inefficient. Red LEDs are far more efficient.

Irv

[Pobboravsky]

Hi Simone and Festus,

Festus, perhaps you meant sodium sulfite rather than sulfate. I don’t know the effect of sulfate on the time it takes to remove silver iodide from a plate. Sodium sulfite should be used with sodium thiosulfate in a fixer. The image of a Becq. plate consists of metallic silver particles of various sizes — all of them quite small. Fixing a plate for a long period of time will first dissolve the smallest silver particles and with enough time reduce the size of even the largest particles. In other words it will weaken the image. An

Quote:

Iodine magenta/purple first cycle

should clear in under a minute and can be kept in the fixer for 2 minutes. Adding sodium sulfite reduces the rate of dissolution of the metallic silver particles.

I very much agree that the image is very good. You are making remarkable progress.

When you iodize the plate does the color of the iodized plate show the same non-uniformity as you see in the final image around the edges? If so it provides an early warning that the edges are not clean. I wonder if fixing the iodized plate is a way of cleaning the plate; after rinsing in distilled water and drying – re-iodizing the plate will show if the color of layer is uniform right to the edges. If it is uniform you can use the plate in the camera.

Good Luck, I look forward to seeing continued progress.

Irv

[Pobboravsky]

Hi Simone,

For beginners, these images are remarkably good. My congratulations.

I think the first image is overexposed in the camera since the image began to appear in just 5 minutes of Becquerel development.

The second image seems to be correctly exposed in the camera. Increasing the Becq. development time will eliminate the blue tone.

To arrive at the correct exposure you might consider making a series of increasing exposures on a single plate. First expose the entire plate for say one minute, push the dark slide in 2-cm and continue the exposure for another minute. Repeat the 2-cm movement and 1-minute added exposure until the dark slide covers the entire plate. After Becq. dev. examine the image and select the exposure time that gave the best image. Expose the next plate for the best-image time.

To see the effect of Becquerel dev. time on the appearance of the image, a plate given the correct camera exposure can be given a series of Becq. dev’ment times by a similar method. You can then select the best development time by examining the final result.

Before iodizing the plate must be very clean to avoid the non-uniformities in the image.

You have made a great start on your daguerreian journey.

Bon chance

Irv

[Pobboravsky]

Hi Photolytic,

Excellent analysis! Congratulations.

The 1994 Daguerreian Annual has an article by Emily Bailey and Clyde Barlow on recovering gold from gilding solutions. It is entitled: If Only Alchemy Were This Easy: A Practical Method of Recovering Gold from Used Gold Toning Solution; pp. 13-16.

Never tried it myself but would be interested in the results of anyone trying it.

Irv

[Pobboravsky]

Ken, Ken, Ken, I was shocked to hear you would elect-to-plate your children!

Irv

[Pobboravsky]

Hi Jason,

I say Bravo! as well. For a first image after 2 years it is clear you know what you are doing and the Daguerreian muse was in your court.

Irv

[Pobboravsky]

Hi,

“Keep a good notebook. If you think using bromine complicates the process, thats nothin’ compared to the variables of silver-plating.”

Mike kids you not!

Recovering galvanizer

Irv

[Pobboravsky]

Hi John,

The graph of absorption versus wavelength of AgI came from:

Washburn. E. E., ed, International Critical Tables, N.Y.:McGraw-Hill, 1929, vol. 5, p. 270.

and

Berry, C.R., “Structure and Optical Absorption of AgI microcrystals”, Physical Rev., Vol. 161, no. 3, 15 Sept. 1967, pp. 848-851.

See reference 4 in the bibliography of Study of Iodized Daguerreotype Plates.

All the very best,

Irv

[Pobboravsky]

John,

Thank you. That is more information than I had — how soon we (I)forget — assuming that I ever knew. This underscores why cdags is such an invaluable website. Great job, John

I don’t know of anybody measuring the spectral sensitivity of daguerreotypes.

Irv

[Pobboravsky]

Andy,

If reducing exposure time is a priority the best bet is adding bromine sensitizing and mercury development. Even with an expensive quartz lens I suspect (I don’t know) you would gain just 1 or 2 stops. But if you go the quartz route I would be very interested in the results. If you try a single element quartz lens the image might be fuzzy because the UV and blue light might focus at different focal planes.

Irv

[Pobboravsky]

Andy,

I don’t know. The graph shows that sensitivity is rising at 350nm and one might expect it would get to 320nm but extrapolation can be misleading. I’m curious, why is UVB wavelengths of interest?

Irv

[Pobboravsky]

Re: pinhole experiment to see how much UV contributes to the overall exposure.

I made a pinhole camera with a f/22 “aperture”. (1-mm aperture at a distance of 22mm from the plate) Pinhole apertures are usually much smaller than 1mm but I was not interested in sharpness – only in the contribution of UV to the overall exposure. Sharpness was not important because the test target was a gray scale with large steps. f/22 gave an exposure time of 5 minutes. At that time, the light source consisted of two banks of blue fluorescent tubes designed for illuminating newborns to correct jaundice. The manufacturer’s literature said that UV was filtered out for safety sake. A conventional “white” fluorescent tube was included to make subjects easier to view; blue light is not visually efficient, looks dim and subjects appear weird.

Two plates were exposed, one with a Wratten 2a over the aperture to block UV and other without the filter. The plate exposed with UV + blue light was twice as “fast” as the one exposed with blue light only. UV contributed an extra stop to the exposure for the conditions of this experiment.

This is a very imperfect experiment because the result depends upon how much UV radiation was in the light source. If the light source consisted of 100-watt incandescent bulbs there would be very little UV given off. If I was exposing by New Zealand sunlight UV could make a huge contribution to the overall exposure.

Unlike conventional lenses a pinhole does not stop any UV and is very cheap. One might say it is nothing, really. If others would like to experiment with faster “lenses” one could buy single element quartz biconvex lenses from Edmund Scientific or use an aluminized mirror lens; aluminum reflects UV and is free from the problem of different wavelengths focusing at different focal planes (chromatic aberration).

Irv

[Author]

Posts