Mysterious White Dots on Photopolymer Plates

Platemaking was a challenge yesterday. I had problems with mysterious white dots on my polymer plates. The dots were most noticeable in the midtones and low values. I discovered other users of polymer plates have experienced similar problems so I tried various techniques I found online to resolve the issues to no avail.

A phone call to Aaron Bass at Takach Press got me back on the right track. One approach involves increasing pressure in the vacuum frame, the other involves heating the plate prior to exposure.

The pressure in the vacuum frame was increased by adding a layer of felt to the bed of the vacuum frame in the exposure unit. This suggestion came from Aaron Bass via Regina Held, of New Grounds Print Workshop. After adding felt to the bed of the vacuum frame, I ran a test plate and saw a big reduction in the white dots on the plate but they weren’t completely resolved. The next step was to warm the plate prior to exposure, following Aaron’s suggestion.

To obtain even warming, I employed the use of my dry mount press. With the heat set at 275 degrees, I placed the plate on the bed of the dry mount press emulsion side down and let it warm with the iron in the up position. Enough heat was generated between the bed of the dry mount press and the iron to heat the plate evenly without melting the plate. I ran another test plate with the felt and warmed plate. While there was a significant reduction in the dots using the two techniques, I still saw three rogue dots.

On a whim, I decided to apply baby powder to the non-emulsion sides of the aquatint screen and transparency. Previously I had only dusted the plate and the emulsion side of the transparency. This additional dusting completely eliminated the dots when combined with the layer of felt and plate warming.

My first plate of the day is dot-free but more testing is needed to determine whether these three techniques will provide a permanent solution.