~~~~~~~~ Excerpt from the Guide to Platinum Palladium Photographic Printmaking by Jeffrey D. Mathias ~~~~~~~~
No part of this document may be reproduced in whole or in part without the express written permission of the Author.
created August 1999,  updated December 2000
Quasi Multi-Coating Method

This author has had mixed results from multiple coatings in the past.  A thought was that some of the past difficulties were associated with drying the mixture and then re-coating.  Coatings of mixtures containing 50 % to 100 % additional mixture had been brushed into the same areas without problems.  So, it was supposed that additional mixture could be added to the coating before it dried completely.  (Hence the term "Quasi".)  Keeping the coating moist seems to be the key to successful multi-coatings.
Multi-coating is not required on fabric as the coating method for fabric completely saturates the fabric with a single coating.

The Quasi Multi-Coating Method step-by-step procedure is as follows:

  • Calculate the amount of chemistry needed for the mixture from the area to be coated, the Coverage factor for the paper (which depends on the type of paper, sensitizer and metal selection, and coating efficiency), and drop size (if measuring by drops).  If measuring by drops, use this equation:

    • ([# of drops] = [area coated cm2] / [Coverage cm2/ml] * [ml per drop])
    Or if measuring by pipette use the following:
    ([ml] = [area coated cm2] / [Coverage cm2/ml])
     
  • Dilute the coating mixture with H2O so as to have enough volume for the number of coating layers anticipated (usually this will be double the amount which can accommodate at least three pouring layers).

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  • Pour out an amount of mixture onto the paper as typical for a single coating (usually half of that mixed and diluted).

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  • Brush this into the area desired as if it were a single coating.

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  • Allow to dry to the point of loss of the gloss, but before near dryness of any portion (rather damp).

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  • Pour out some more of the mixture (about half of that remaining).

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  • Brush this into the area desired as if it were a single coating.

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  • Allow to dry to the point of loss of the gloss, but before near dryness of any portion (rather damp).

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  • Pour and brush the remaining mixture as if it were a single coating.

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  • Dry to desired dryness for the "Wet" (POP) or "Dry" (DOP) method.
    • Each pouring should be enough to completely coat a layer over the full area.  Do not extend any mixture beyond the area.  With this Quasi Multi-Coating Method, it is of the utmost importance that the coating be restricted to the correct area.  Spreading the mixture too thin (past the area) will result in a weakened coating which, if below the threshold, will produce a weakened print.  Not spreading the mixture to fully to cover the area will result in a stronger (is places) but incomplete coating.

    A coating  mixture with five pouring layers (5 quasi coats) has been accomplished taking a little more than half an hour to coat and dry.  This produced excellent prints, although additional texture could be felt on the surface of the paper.  Similar quality prints were achieved with only the three pouring layers suggested without any roughing the surface texture of the paper.

    Drying times are significantly lengthened with multiple coats.

    If an initial pouring layer is allowed to get too dry, lighter blotchy areas may appear in the final print.
     

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