caparol: finally a success!!
oh my ... IT WORKS!
i seriously did not expect this. after this mess, which i wasn't able to find a way out, now this. same emulsion as before prints beautifully.
my gum woes were size-related after all...
caparol binder comes in batches of 1kg and 5kg, the 1kg package cost me 13.50euro (gerstaecker is cheaper than that!). it should be available from most arts suppliers around europe. i has a milky consistence, similar to glue. i'm not sure if this will be compatible with sizing above pre-existing layers, like gum-overs (according to the data sheet it's supposed to dry completely clear).
i've read somewhere (can't find it now) that an canadian conservation institute recommends pv-acetate grounds as preferable to the classic rabbit skin glue for oil painting. so archivality is hopefully no concern here.
pic of the package:
one test strip was sized with caparol binder diluted 1+1 with water. the other one with a 1+5 dilution (i've read that this is the correct dilution for using it as a ground).
both sizes were one-coat, brushed on with a simple brush. dried for appr. two hours. i took a shower next to the drying strips, so it's probably not too sensitive to humidity... haha.
brush strokes are somewhat visible in the size.even minimal stain can make these these brush strokes unpleasantly visible. the 1+5 is a pretty watery solution, depending on the keeping qualties, maybe immersion sizing could be possible.
the emulsion was: 5ml 33% gum + 5ml sat.pot-di + 1gr iron oxide black (the same mix, that stained horribly before)
it does coat surprisingly well. no major fisheye-action. but it doesn't coat as easy as a gelatin size. as you can see in the scan the brush strokes are visible, i think this needs a refined brush technique and some practice. the test strips were coated with a broad synthie brush and smoothed with a hake.
the 1+5 strip did definitely coat smoother and looks better dried too. with the 1+1 strip i noticed some puddling and minor fisheyes, but all brushed out easily.
pic of the coating pre-exposure:
(1+5 = left, 1+1 = right)
left side: 1:20min;right side: 3:00
the times were total guess work, since i haven't made a successful gum print in weeks, let alone with the new dichromate.
the 1+1 test strip was developed for 20min, the 1+5 for 30min.
the 1+1 size does clear noticeably quicker and has no stain. the 1+5 does have some stain in the area with zero exposure (this stain can easily wiped off, as you can see in the area where i rubbed my finger on), but i can't see any in the highlights of the chart throb scale. in both cases the highlights look brilliantly white.
in the areas where the emulsion puddles a little (thicker areas of emulsion, which were not completely hardened through) there is some minor flaking. in the 1+1 strip this is visible in the coating, in the 1+5 coating this only happens in the area outside the image, where the brush is put on, or the brush turns around.
i'm not completely satisfied with the finer tones, especially in the 1+1.
in conclusion, there are some difficulties, but i expect them to be manageable. i'm very happy that i'm out of the mess that i had last week, a huge load off my mind. and hopefully this means an end to gelatin and stupidly toxic hardeners for me.
this was a first (quick and dirty) test and not my final word on the size. but it does look promising. i will try a 1+10 dilution (maybe two coats)- for maybe a little more stain, but better highlights.
tests to follow: real images, different papers, different dilutions, on wood and on canvas.
i have ordered two other sizes, which i will try later, next week or so. one (ingredients still unknown) is significantly cheaper than the caparol. the other one, the "liquitex clear gesso" is based on some form of acrylic after all- so this one was probably wasted money.