Silver Rich - Silver Poor - ?

Discussion in 'B&W: Film, Paper, Chemistry' started by dancqu, Apr 28, 2007.

  1. dancqu

    dancqu Member

    Messages:
    3,676
    Joined:
    Sep 7, 2002
    Location:
    Willamette V
    Shooter:
    Medium Format
    I took some time out to check the densities of two
    print papers complete with 21 step step wedge imprint.
    I used my Tobias Transmission densitometer equipped
    with the 3mm aperture.

    First surprise; Both the Kentmere Fineprint and Forte
    Polywarmtone had the exact same base densities; 1.17.

    Second surprise; Depending upon where the line
    is drawn, we are at the shoulder now, the Fineprint
    topped out at 1.30. The Polywarmtone made it to at
    least 2.45. Both those figures are above base.

    That's a BIG difference in Transmission density.
    Visually the reflection density favors slightly the
    Polywarmtone. My conclusion; Poly is silver Rich
    and Kentmere is silver poor. Could there be any
    other explanation? Dan
     
  2. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

    Messages:
    4,351
    Joined:
    Apr 2, 2005
    Location:
    Montréal (QC
    Shooter:
    Multi Format
    Ouch! Can of worms alert!
     
  3. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,770
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Yes Dan, there can be several answers to the question. It can be due to the morphology of the silver developed, the thickness of the paper or Baryta or any one of a number of other factors.

    A milligram of silver metal per square meter does not always give the same density from different emulsions, nor does starting with the same laydown of silver halide give identical densities when development is complete.

    In addition, some papers have additional shadow density that cannot be seen by reflection but the transmission density is changing, so you cannot see it but the densitometer (by transmission) can.

    PE
     
  4. Ryuji

    Ryuji Member

    Messages:
    1,416
    Joined:
    Jan 15, 2005
    Location:
    Boston, MA
    Shooter:
    Multi Format
    You can't compare silver content by optical density across different emulsions. Depending on the crystal technology and gelatin additives, the optical density varies a HUGELY even if the silver content is constant.
     
  5. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,770
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Dan;

    I've thought this through overnight and here are some additional comments.

    Since the effects of transmission vs reflection density are non-linear, it is often hard to relate what you see or percieve to the two types of readings. In addition, the way of coating on baryta affects the percieved density vs the real density. Sometimes, the emulsion can 'seep' into the baryta during coating and this changes the effective viewing and transmission densities measured.

    Viewing angle is important with some reflection materials, and not as much with others. This variation vanishes when you use transmission measurments.

    One way we had at Kodak to try to damp out reflection vs transmission variations was to measure strips of FB paper that were soaked in mineral oil for reading by transmission.

    This treatment rendered them partially translucent and allowed better readings (sometimes). Please see my comments about silver rich materials in the Emulsion making and coating forum.

    PE
     
  6. dancqu

    dancqu Member

    Messages:
    3,676
    Joined:
    Sep 7, 2002
    Location:
    Willamette V
    Shooter:
    Medium Format
    By base densities I mean the paper's unexposed areas.
    By any chance are the two papers coated on the exact
    same base; exact same paper?

    On transmission the Kentmere paper's most dense areas had
    a translucent character and definitely cold. The Forte paper's
    most dense areas had more of an opaque character and
    not at all cold.

    Warm tone papers are sometimes associated with a fine
    grained image structure. Perhaps that finer grain also
    accounts for the very decided greater Transmission
    density. The Kentmere was about a stop faster.

    I wonder if anyone has ever been tempted to use
    a black backer mat. Perhaps it would pull the
    highlights down. Dan
     
  7. Photo Engineer

    Photo Engineer Subscriber

    Messages:
    25,770
    Joined:
    Apr 19, 2005
    Location:
    Rochester, NY
    Shooter:
    Multi Format
    Dan;

    Maybe they are on the same support, but consider this. What if one was coated directly on the baryta and the other had a thick gelatin size coat under the emulsion layer. This would lead to an entirely different look between the two papers. At least this is my experience due to the extra layer above the baryta.

    They probably both use Schoeller papers from Germany, but IDK for sure.

    Warm tone papers are certainly different emulsions than cold tone papers, but often even different baryta is used. At least it was at Kodak. Warmtone papers had just a hint of a beige tint to the baryta in some cases to enhance the warm tone.

    In any event, it is the mass of silver developed that is significant, not the amount of silver coated. In many cases, most of the silver of whatever level is washed out in the hypo and wash steps.

    PE