Category: alt photo

friday: Collected Maybe

Posted on Posted in alt photo, collotype, labnotes

many small readings. short hand notes.

st/ages of theory: how-to / what / why

learning from the hobby lobby means you may never know a reason. you probably won’t ask them questions, after-all, you and they are just hanging onto each other’s opinion. You will never ask where he saw that work. Unless you remember, because you were a member of the academy, you wouldn’t realize that geography was a strong barrier to exhibitions in the 70s and 80s.

Dichromated Gelatin

ask the other camps. look in books and journals. maybe google has a bigger, better memory than you realize.

The advantages of Dichromated Gelatin over Silver Halides are:

  • More efficient recording material.
  • Has less scattering.
  • Is more transparent.

as dichromate is exposed absorption spectra changes.

the broader the exposure spectrum, the deeper the hardening reaction.

characteristics are listed below.

  • Initial thickness of the gelatin layer
  • Initial hardness of the gelatin
  • Concentration of sensitizing dichromate bath
  • Drying conditions: temperature, humidity, and time
  • Exposure, wavelength and energy
  • Time delay between exposure and processing
  • Alkalinity and temperature of processing baths
  • Composition of processing baths
  • Time in processing baths
  • Recording geometry

Factors Influencing Light Geometry

(a) Size of the light source. The larger a source, the greater becomes the angle of light rays travelling from its edges and therefore the degree of undercutting.

(b) Position of the light source. The nearer a light source is to the vacuum frame the greater is its effective size. Conversely if the lamp is moved further away, so its effective size is reduced. It is good practice to increase lamp distance when exposing very fine detail work to reduce the effect of light undercutting if at all practical, (do not forget that the exposure time will have to be adjusted if an integrator is not fitted).

the “printing out” tanning is similar in contrast effect as the “developing out” of tanning developers. DAS / Dichromate systems share the exposure effect: judge by depth of “cure” — tanning, hardening of the colloid. DAS exposure should begin with 365nm wavelength.

Absorbance and sensitivity are different. This is partial explanation for why color of exposing light should be broader with a longer (more depth) exposure requirement.

Lost Highlights

Posted on Posted in alt photo, dye transfer, labnotes, morning wood, pipeline, the fora

highlights can be washed away or crushed in assembly — huh? Okay, they can, but not if you are making dye transfers correctly.

Dye transfer was used by commercial photographers doing flatware, silk goods, diamonds, crystal — it seemed good enough for those highlight intensive products photos used for point of purchase along with sample books.

Dye transfer was used by portrait photographers selling upscale bridal portraits for their wedding — the 20×24 for the family to remember the bride in her white wedding gown. Another highlight intensive requirement.

Further examples seem unnecessary. The large-format dye transfer expert isn’t experienced. Sadly, those involved in that conversation don’t know enough to know — maybe they just don’t care, since they’ve nothing else to do. It is after all, only chat among the idle — an endgame move of resignation.

Why do so many believe the persistent posters?

The difference between a carbon print and a dye transfer is extreme. That they are assembly processes using gelatin as the image carrier, and that the image is a result of differential hardening of gelatin is what they share. Exposure method is a major factor in how highlights are maintained or lost.

In pigment processes exposure is from the top of the emulsion/coating. In dye transfer (imbibition ) exposure is through the base; this means the gelatin is hardened from the support upward. The highlight is thin but it is close to the support. In carbon the highlight tends to wash off, since it is being dissolved away. The pigment will actually collapse. The dye transfer mat has a relief image but it is durable. In imbibition printing the final image is assembled in thin layers; in gum/carbon it is stacked up in thicker reliefs. This can, likely will, result in some undercut of fine color details which occur alongside larger detail areas. In an effort to reduce this problem, screened negatives are being used by some carbon printers.

Dye transfer has additional controls to manage highlights which provide even more advantage over carbon printing. Carbon’s advantage is the tissue is easier to make than matrix film. Carbon rules because it can; it’s’ disadvantages have been made a part of the aesthetic feature: lots of “dimensional” texture.