[Alt-photo] Outgassing in contact-printing siderotypes
workshops at polychrome.nl
Mon May 19 11:12:31 UTC 2014
I can confirm this. When printing ferric carbon, with Halvor Bjørngård's Chibatype , I am using yupo as coating subtrate for the pigment tissue. Yupo will not let the carbon-dioxide escape through the back of the tissue. While printing I am using a thin melinex sheet between the digital negative and the sensitive gelatin layer. I am exposing with a large home build vacuum frame with 6 mecury-vacuum (HPR) lamps. After exposure I can clearly see the melinex bubbling. In the image itself it is not visible. Maybe because of the HPR lamps,which are point light sources, allthough I use them in two rows of 3 lamps above my 120x70cm frame, making the overall light somewhat more diffuse. With paper based processes like (classic) cyanotype, van dyke or ferric caseïn I never saw this outgassing happen.
I will do some more testing with a diffuse UV TL bank and my Eskofot plateburner.
Currently I am working mainly with diazidostilbene (CAS 2718-90-3) sensitized carbon tissue.
Some people also observed some sort of outgassing there. I do not. And it probably was not carbon-dioxide.
On 19 mei 2014, at 12:16, Mike Ware <mike at mikeware.co.uk> wrote:
> Regarding siderotype (iron-based process) contact-printing, there seems to be a technical issue, previously unrecognised, which I would like to share and invite comments.
> During the exposure of all siderotype sensitizers - no matter which process - there is an evolution of carbon dioxide gas, which needs to find a pathway to escape through the back of the paper.
> Otherwise it forms bubbles trapped between the negative and sensitized paper surface; a simple calculation suggests that the resulting gap can become large enough locally to blur the acutance or resolution of the contact-printed image. This is confirmed by my tests.
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