Saturday, March 21, 2015

Good example of how the spread has improved, and what still needs to be done.

The spread, or how the reagent - that thick, viscous processing semi-fluid paste - travels in between the negative and the positive sheet, is not an easy thing to control.

Several factors contribute to the success or failure of the spread.

  1. The stack up of the layers. How thick each part is.
  2. The flexibility of each part. Negatives are stiff, paper can be stiff, the outer sleeve and the tongue have different, designed-in stiffnesses. Nothing about them is an accident which is what makes it difficult to source the materials.
  3. How that stack up sits evenly or not under the high sides of the rollers. The rollers aren't flat. Look next time you open a 545 and you will see that one of the rollers has higher areas. This was intentional and done precisely to accomodate the Polaroid process. New55 is different and yet still has to work in these same rollers.
  4. The rate of pull. A user can ruin the spread by pulling too quickly.
  5. Temperature. If it is cold, the reagent is stiffer, and spreads poorly. Better to go indoors and warm up.
  6. Condition of the holder. Rarely, these are damaged or worn.
  7. The pod contents. Is it filled with exactly the right amount of reagent?
  8. The pod seal. Does the seal burst in just the right way?
All of these have to be just right or the system won't work. Here are some effects and causes when things aren't right:

Spread too thick: The reagent won't cover the entire surface. This is caused by improper stack up distances, but an incomplete spread can also be caused by a bad pod. A too-thick spread can be identified on the positive print because the image will have poor sharpness.

Spread too thin: Usually perfect coverage, but the negative won't fully process and will be mottled. The positive print will be extra sharp, but a too sharp positive means a very tight gap which does not allow the full cycle of developing and fixing to occur on the negative side.

Below are examples of a spread that was almost right, but too tight for a perfect negative. Note the mottling in the mid tones of the chart. The positive print looks OK. This is considered close but not good enough. A wider gap might cause the spread to be incomplete, which would affect the pod fill. 

 Positive print. Looks OK, decent spread, and
 excellent sharpness. Very slight mottling can be seen
in the mid tones. Coated Jan. 15. '15 and shot Mar. 20, '15.

The negative. Despite good coverage, the mids
are seriously mottled. Not enough goop. Mar. 20, 2015.

No comments: