[Alt-photo] Re: Stochastic screening in Gum

[sam wang]

Hi Peter,

With gum, since the negatives' DMax requirements are so low, I've found that almost any inkjet printer would work. The first digital negatives that I used for tricolor gum were made on a very early black and white inkjet printer. However, service bureau stochastic negatives can print much more predictably, and a lot more forgiving in exposure and development because of the hard dots. But I gave up trying to find a service bureau that can do so and not too expensive.

To create stochastic patterns with Photoshop is not hard, just select diffusion dither in the bitmap options. You'd get interference patterns in the exact mid-tones in some cases. For inkjet there really is no need for it anymore. But after tearing my hair out from inkjet printer problems, I tried using laser printers (as answer to another thread) - it worked OK, if you don't mind fairly bold and obvious dot patters. I find that more attractive than the usual halftones you get with laser printers. I've always wanted to make some really graphic gum prints by lowering the lpi, and use lines instead of elliptical dots, but never got around to.

As to minimum dot size, I don't have answer as to inkjet, but on service bureau negs using dithered patterns from Photoshop, I could only get 635 dpi predictably. That's limitation by the printer, not gum.

Hope this helps.

Sam Wang


On Dec 6, 2013, at 6:21 PM, Peter Friedrichsen <pfriedrichsen at sympatico.ca> wrote:

> Has anyone applied a stochastic screen to gum printing? This is a half tone technique that uses dot frequency to emulate color/greyscale. The smaller the dot size, the more photographic the rendition. My UV box generates diffuse UV light so I think that may not be as effective as a more point sourced arc type UV lamp.
> 
> Has anyone done anything like this before? I was wondering what the minimum dot size that could be realized from a contact negative?
> 
> Peter Friedrichsen
> 
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