Re: Gum Color Gamut & Beyond CMYK?

[Katharine Thayer <kthayer@pacifier.com>]

See my page on tricolor gum printing

http://www.pacifier.com/~kthayer/html/tricolor.html

for a brief consideration of this topic (scroll down the page to the  
subheading, "Is it possible to reproduce the entire spectrum using  
three color layers?" )

The answer, from Bruce McEvoy, is no,  you do need to add the  
secondary colors (in other words, in gum printing, use six layers  
including the secondary colors in addition to the primary colors, in  
order to produce accurate colors throughout the spectrum,  and I  
suppose some sort of  profiles as Jacek suggests might be the way to  
generate the color separations for the secondary colors.  But this  
seems to me an enormous effort and possibly a misplaced effort to  
boot; if you're looking for this kind of color precision, gum may not  
be the right process for you.  Not that I would discourage anyone  
from dedicating themselves to this kind of study if it appeals to  
them, just that for me and my house, I don't quite see the point.

However, the purpose of the extra colors and separations, as I  
understand it,  is not to extend the gamut so much as to refine it.   
Depending on the pigments you choose as primaries, the layered color  
mixtures will produce different palettes of greens, oranges and  
purples; generally when printing tricolor we pick three primaries  
that give us the kind of secondary mixtures we want.  For example, I  
generally prefer ultramarine or prussian blue for tricolor because I  
don't like the greens that pthalo produces with almost any yellow,  
they look unnatural to me, and since I print a lot of landscapes with  
trees/leaves, I want a more natural looking palette in the greens.   
Adding the secondary colors to produce six layers will theoretically  
make it less necessary to pick and choose primary pigments to produce  
the kind of secondaries you want, because you can choose the  
secondaries to your liking.  But like I said, this seems a heck of a  
lot of work, when three colors, chosen carefully, will almost always  
give us a palette that  gives us a reasonable enough approximation of  
realistic color, with special attention to producing the secondaries  
that we're most interested in.

Katharine




On Sep 20, 2008, at 9:11 PM, Jacek Gonsalves wrote:

> Hi all,
>
> Just continuing what Loris was talking about in regards with using  
> a predefined set of pigments and building a profile for Gum  
> printing. If one could build the profiles based on the CMYK  
> pigments, can we say that this holds a certain color gamut. Lets  
> say we want to increase the color gamut?
>  There are other methods as Pantone Hexachrome method of 6 color  
> separations CMYKOG, adds orange and green separation. Adding these  
> additional separation would therefore increase the color gamut.  
> That is if the image you have includes those additional colors.
> I'm sure there are methods to make additional separations in PS,  
> though it might be complicated? If someone knows how to do this  
> please chime in..
> Though it excites me to think that one could increase the color  
> gamut from finding what pigments fall further than the usual inkjet  
> printers do these days.
> Regards
> Jacek