Na2 Concentrations with Double Coating

[Paul]

Hi,

If I intend to double coat using a full strength coating of sensitizer for the first coat and 1:1 dilution of sensitizer and distilled water for the second coat, how do I handle the addition of Na2 on the second coat? Lets say that I need three drops of 5% Na2 for the first coat. Do I add 5 drops of 2.5% solution for the diluted second coat on the assumption that this will give me roughly 1/2 the concentration of Na2. Obviously, if I needed two drops of Na2 for the first coat, I could just use one for the second. It is when things are in between that it gets confusing.

I would also like to ask what experience people have had in contrast increase between single and double coating. I just made a print that looks pretty good on Cot 320 using three drops 5% of Na2 and exposing for 12 minutes. My thoughts were to double coat with only two drops Na2 in the first coat, and only one drop in the diluted second coat, on the assumption that this would compensate for the increased contrast I expect from double coating. Obviously, I will just try this and see if it works, but I was wondering if there is a more scientific way of dealing with these things when working with droppers.

Thanks for your thoughts,
Paul

 

[sly]

Beats me! let us know how it works.

 

[Lukas Werth]

I would first coat with the weaker, then with the stronger solution, or keep them equal. I think you may add the whole amount of NA2 into any one, it won't make a difference. I once noted after coating that I had forgotten to add AFO to the sensitizer, I brushed it on, and the print exposed just normally.