Just one thing to your remark of raising temperature to 50 degrees; i used the rabbit glue -if you buy it by BOESNER i could be same stuff you use- for preparing inkjet paper, and temperature is critical in that sense that over 40 degree C blistering could be a problem.
What i read about it, was to raise temp. to 60 degree C and when using it, go down to 40 degrees.
after a few weeks of trying, i finally get more or less acceptable results. now it's time for the fine tuning.
i think most of my problems lie in the preparation of the digi negs. i read in the sandy king article that carbon needs a more contrasty neg that gum, so i printed a few small ones with the "strong contrast (rgb)" preset of photoshop.
not the best of ideas, because it has too little shadow density. the areas of the negative that have good density are those that print rather well (f.e. the side of the car in the pic at the bottom), but the thin areas are those that trouble me.
i have the same problem with gum occasionally. even though the contrast range is not big, the dark areas often lack detail. how do i get more guts in the shadows? alternativephotography seems not to have a curve suggestion for carbon? how do you treat your images before printing? curve or straight?
on a related note:
is it possible that photoshop loses shadow detail when inverting an image? scatterbrained as i am, i often forget to invert an image before printing it. this happened again a few days ago. so i printed the same images again, only inverted. and compared there is definitely more detail in the shadows on the positive on film than in the neg on film. for example the stacked wood in the second pic, in the shadow part i can see a little detail (very faintly the pattern of the ends of the logs), while the same area in the negative on film is completely blank.
my guess is that the printer can't print those very faint areas, so they just get lost between photoshop and printer.
my last problem is that there is some kind of fogging, that only seems to happen in the densest areas of the print. it's clearly visible in the two scans (actually it's more visible than in the original). i think it has something to do with the warm water development. i think the excess gelatine comes off the shadow areas first and later off the lighter areas, so those dark areas are exposed to the warm water longer than the light areas. so more pigment floats off and these cloud-like grey areas are produced.
i already tried raising the temperature of the warm water bath to get a quicker development. i used appr. 50°c (120F) in the second pic (the one with the stacked wood), the grey fog is less, but not completely gone.
and regarding relief:
if i want to have a more relief in the final print (i have pretty much none right now - at least nothing tactile when sliding my finger over the print). the clue to relief seems to be a thicker tissue. but does it also mean, that i'd have to expose longer?
the two prints:
both are on homemade tissue (glop: 20gr rabbit skin glue + 15gr sugar + 3.5gr lamp black (powdered) + 250ml water)
spirit sensitized with: 2x 4ml per 8x10 (20ml acetone + 20ml 2.5% dichromate sol.)
exposure: 1:30min; 2 min soak; 19 min press.
exposure: 1:50; 2min soak; 27min press. the one with the increased temp in the warm water.
(contrast is way off in this one)
both images are still inverted because i'm heading for double transfer.
any ideas for improvement?