Coating Paper

step-by-step Procedure: Preparation Humidifying Brushing Drying DOP Drying POP

Coating can make or break the process.  There is nothing mystical about coating, but one must practice coating.  Only after coating several hundred prints may this simple technique be mastered.  Coating technique and ease will vary from paper to paper.  It is strongly suggested that one begin with an easy to coat paper; learn to coat it well; then maybe try another paper.  It is to be expected that various papers will coat differently.

Preparation Steps:
 

Ambient work area preparation differs for DOP and POP and is an important step for consistency and quality.  (See the Wet Dry Drying Study.)

• For DOP, the temperature should be kept below 70^oF and the relative humidity (RH) below 40%.
• For POP, the temperature should be kept below 70^oF and the relative humidity (RH) between 40% and 70%.  Variations in the RH can change the color of the print, in genaral producing a warmer color with lower RH.

Have brush soaking in a dedicated tray of H2O.

 

Have coating mixture ready in shot glass.

 

Have paper ready with the desired side up (see Raw Materials - Substrates - Paper).

 

Mark on paper the area to be coated with pencil dots at corners.  Or, if paper is thin, place old negative of same size under the paper as a guide.

Note: After some practice one should be able to coat the correct size without guides.
           However, it is critical to restrict the coating to a given area.
 

With brush well soaked in dedicated tray, remove it from the H₂O and squeegee between a clean paper towel.

 

Take most of the H₂O out of the brush, but leave damp.

Note: This procedure is intended to keep the coating mixture from being sucked up
           into the brush (dry brush) or from being diluted (wet brush).

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Humidification Steps:
 

Humidify the paper by holding and moving paper over a sonic mister so that the front is humidified, then so the back is humidified, then so the front is humidified again.

Note: Do not get the paper soggy.  Do not get water droplets on the paper.
           Do let the paper become humidified so that it just loses the crispness felt or
           heard when bending.
Note:  Some thin papers may not require humidification.

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Brushing Steps (illustrations below):
 

Place paper onto the coating work area desired side up (use a pad of newsprint or plastic sheet to keep spills or overshoots off the table).  (figure A)

 

Pour the shot of coating mixture in a line well inside one edge of image area. (figure B)

 

Get all of the mixture out of the shot glass, with brush if necessary.

 

Run brush down the line of mixture and spread.  (figure C)

 

Brush mixture across the paper perpendicular to the line.  (figure D)

Note:  The previous four steps should occur as rapidly as practical.
Note:  Hold the brush at an angle of about 30^o to the paper and pull along gently,
            but swiftly.
 

Brush mixture in direction 90^o to last brush direction.  (figure E)

 

Brush mixture in direction 90^o to last brush direction and opposite to the first brush direction.  (figure F)

 

Brush mixture in direction 90^o to last brush direction and opposite to the second direction.

 

Repeat brushing in all four directions once or twice depending on how fast the coating mixture is soaking into the paper.  (figure G)

Note:  Stop brushing immediately when some drag is felt.  Brushing beyond this point
            can abrade the paper and show as a textured spot in the print.
Note:  Coating must be quick and gentile and cover the entire image area.  If not quick
            the mixture may be lost into the paper.  Make sure the mixture is brushed
            thickly over the entire area.  When coating is thin the image will be weak.  Don't
            waste the chemistry by brushing it out of the image area.
Note:  Do not let the mixture soak through the paper.  This may hurt the uniformity.
            Also, do not let the mixture puddle, as this will also hurt uniformity.
Note:  Surface brush marks in the coating should not matter as long as the coating is
            solid.
 

Place brush and shot glass into H₂O bath (dedicated tray).

A                       B                       C                       D                       E                       F                       G

Coating paper by brush: (A) everything ready; (B) pouring the solution; (C) initial spreading; (D) brushing across paper; (E) brushing at 90^o; (F) brushing in next direction; (G) brushing in next direction on repeat.

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Drying the Coating:

Drying methods differ for DOP and POP.  Be sure that the ambient conditions of the work area are stabilized at the desired levels within parameters above.

Coated paper wet (left) and dry (right).

Drying steps for DOP:
 

Let the coating air dry until the glossiness goes away.

Note: Paper may be lifted and turned to prevent puddling by gravitational distribution.
 

Dry front with hair dryer at settings of high blow and low or medium heat.

Note:  It is desirable to use heat, but do not get coating too hot (more than 140^oF
            may do damage.)
Note:  Puddles dried will show the edge and be blotchy.
 

After front is completely dry, turn over and dry the back, then dry front again.

Note:  Coating must be "bone dry" for exposing.
Note:  Coated paper might be stored for up to an hour.  Dry once again immediately
            prior to exposing.  Never store for longer than 4 hours.
Note:  The coating will depreciate with time; so, no matter how it is stored, it will go bad.
Note:  Do not let any liquid, or drops, or spray, or fingers touch the coating, because
            doing so will leave a mark in the print.

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Drying steps for POP:
 

Immediately dry with hair dryer at medium or high blow and NO HEAT.

Note:  DO NOT use heat as it is imperative that the coating and substrate obtain the
            relative humidity of the ambient.
Note:  Be careful so as not to cause any puddling of the chemistry.  There is no time
            to wait until glossiness goes away as with DOP.
 

Drying should take about three or four minutes.  The goal is to get the paper and coating to the ambient relative humidity.

Note:  If too much time elapses from end of coating, through drying, to exposure,
            adverse effects may occur such as graininess.
Note:  To check when drying is complete, a finger may be lightly moved across
             the coating.  When smooth and not sticky, the coating should be at the
             proper dryness.
Note:  Too much drying will result in a warmer color (color may be blotchy if the drying
            is uneven).
Note:  Expose immediately; do not store.
Note:  Do not let any liquid, or drops, or spray, or moist fingers touch the coating,
            because doing so will leave a mark in the print.

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