Re: How many gum layers (Re: ferri sesquichlorati)

[Katharine Thayer <kthayer@pacifier.com>]

On Oct 25, 2006, at 9:27 AM, Keith Gerling wrote:

>  " Otherwise, why not just start with an image, invert it and make  
> a negative of any unknown density without a curve and keep fiddling  
> with it until you get what you want in the print."
>
> Best Wishes,
> Mark Nelson
>
>
> Well, Mark, that is exactly my approach and it does seem to work.   
> However, having been challenged by recent workshop participants as  
> to why NOT use a curve of some kind I admit that I have been  
> fiddling around with curves lately and have found that the curve  
> that works best for me is a straight line, i.e., no curve at all.   
> So I'm curious.  Are there list members out there that DO use  
> curves for gum printing?  Might one of them be persuaded to share  
> their curve with me so that I can try it?  I'll figure out some way  
> to repay a kind soul for this generosity.
Keith, I'm not sure it would be helpful for someone to "share their  
curve" since it's my understanding that a curve is specific to a  
specific emulsion and printing conditions.  So the curve I've been  
developing is only for Prussian blue (and probably M. Graham Prussian  
blue at that) at a specific gum/pigment ratio,  mixed 1:1 with  
saturated ammonium dichromate, and printed on Arches bright white  
sized with gelatin and glyoxal, under an EBV photoflood for 2  
minutes, at a temperature of 60 degrees F  and 75% RH, from an inkjet  
negative printed on the specific kind of cheap transparency I'm using  
(whatever it is).  Any deviation in that protocol would necessitate  
drawing up a new curve, because the curve is intended to fit the  
protocol exactly.

Katharine