Coating emulsions on paper support

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, Dec 16, 2007.

  1. Photo Engineer

    Photo Engineer Subscriber

    Apr 19, 2005
    Rochester, NY
    Multi Format
    I have had a lot of notes from people wanting to coat on paper support or those who have tried with poor results. So, I thought I might add some comments.

    First, it is well to consider that Baryta is harder to coat on than hot press paper, and hard press is harder to coat on than cold press. At the same time, the lower the weight, the harder it is to coat. I limit myself to 100# or higher and hard press or baryta.

    Next, you should know that you can coat on hard and soft press paper without a surfactant most of the time, but you will need a surfactant and probably an extender for Baryta. If you don't, you will get repellancy spots or circular areas in which there is no coating. They look like craters. You can also get streaks.

    If you make the coating temperature too high, the emulsion will puddle on the surface, and the paper will curl or buckle. A low temperature is best for coating paper support and it should remain untouched until it begins to look matte on the surface.

    If you use a puddle pusher or any spreader without a well to contain the emulsion, the emulsion itself will cause the paper to swell as you pour it on the paper, and it will thereby cause a "V" shaped defect at the start of the coating due to swell. The swollen paper raises up to touch the puddle pusher and they mutually scrape away the emulsion.

    Other alternatives exist to coating blades. You can use a tray and soak the desired surface face down in the melted emulsion in the tray. Then, lift a corner and gently drag the paper evenly and squarely over the tray edge using the tray to scrape off excess emulsion.

    Remember that brushes, both bristle and foam can be used, but the former leaves brush strokes and the latter tends to create bubbles. These are both quite ok and can add an art like texture to the coating, but you will need about 2 or 4 coats at right angles to each other to get a good cover.

    And, the coated surface must always be larger than the desired print by at least 1/2" or so to allow for handling and edge defects.

    I hope this addresses most of the quesitons that I have been getting in one place. Also, remember that this is an art form that requires practice.

    I practice with 8 - 10% gelatin with food dye in it (about 2 - 6 drops / 120 grams of melted 10% gelatin) so that I can see the results of my work. Remember that food dyes contain additives and the best are liquid dyes in dropper bottles, not the gels in tubes.