Re: Dichromate dilution and speed

Sandy,

Do you know to what baume Sam mixes his gum solution? Isn't baume a measure of specific gravity? If it is, I would assume that the 14B standard adequately takes into account the quantity of dry gum in the mix, unless there are heavy gums and light gums. If that is the case I would assume variations in the purity or density of the colloid from year to year would make a much larger impact on the printing and would be something that couldn't be easily standardized regardless of the amount of dichromate used. What would be a better universal measure for gum, liquid or dry, than baume? Where and when the gum was obtained would influence the process a great deal as several others have pointed out in the archives (most recently Katherine in her discussion of P. Formulary gum).

As an aside, with gelatin do you find differences in bloom make a difference in carbon printing characteristics? Perhaps differences in baume make for more or less success with gum.

I also think perhaps the nature of the digital negative (on/off vs. continuous tone) impacts the results Chris reports. Also, she mentions her use of the Edwards exposure unit vs. Sam's use of the NuArc. I'd again mention the fact I get much better results using the potassium salt and a quartz halogen source or the sun rather than UV fluorescent tubes (which I assume are in the Edward's unit). I recently acquired a NuArc Mercury 124K (?) unit which I've used with some initial success with gum. It appears to print with an overall quality similar to the quartz source.

I think Sam's results are outstanding, but I really do not think using dry dichromate for each emulsion mix is safer than using precisely diluted dichromate solution. As far as lessening personal exposure and ease of measurement, I would prefer using the liquid. I think everyone involved in this thread is saying that the amount of dichromate and gum and water can be quantified and controlled various ways, just how we choose to do the mixing and measurement differs. Aren't we really discussing where and when the water goes into the mix rather than how much total we add?

I also vaguely remember reading a statistic which stated the industrial discharge of dichromates into the environment was several thousand metric tonnes daily. (Actually I think it was more like tens of thousands...) I'm reasonably confident the minor amount we gum printers discharge into the environment is inconsequential in the greater scheme of things, especially if we take care to neutralize the hexavalent compounds before we flush them.

Joe

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Received on Sun Nov 30 22:32:27 2003