Blisters or bubbles in home made paper emulsion

[Cor]

Seconded - that's a very long dev time for a handcoated, non supercoated emulsion - in fact, I think the fogging that @Cor is seeing probably is general fogging from excessive developing time - a minute is usually plenty even at normal working strength.


There are some interesting complexities in the handling of coated, unhardened emulsions - Shanebrook has some references to how it was tackled industrially.

Quickly summing up Ron's segment on hardeners, he categorises as following:

Formaldehyde - Very Toxic - Fast Hardener
Glyoxal - Mild Toxicity - Medium Hardener
Succinaldehyde - Very Toxic - Medium Hardener
Glutaraldehyde - Very Toxic - Medium Hardener
Chrome Alum - Toxic - Slow Hardener
Vinyl Ethers (BVSME) - EXTREMELY TOXIC (caps as per original) - very fast, modern hardener, needs special handling in manufacturing (it's so fast reacting that traditional melt & coat methods would cause it to harden en route to the coating head), but safe for the end user of the hardened, coated product.

He states that the Aldehydes may take up to a year to fully react (but are sufficiently hard for processing paper coatings after "about 4 hours") and that Chrome Alum can be so slow acting that some emulsions were made with it already incorporated (i.e. would not gum up the coater). His recommendation of Glyoxal was based off it having a lower vapour pressure than the other aldehydes. I've not had many major issues with Chrome Alum hardening, even after quite short (hour or so) intervals after coating/ drying before processing.

hi Lachlan,

Thanks for the write up, interesting, and also pointing out that my developing times are too long, thus far I processed as per factory silver gelatin paper, learned again !

best,

Cor

 

[Lachlan Young]

Acidic stop bath and acidic fix. Could some thiosulphate be decomposing in the emulsion due to acidic conditions and releasing Sulphur Dioxide bubbles? Thiosulphate decomposition generally requires stronger acid but who knows.

Carbonate buffered developer hitting acid stop was a well known source of blistering on poorly hardened emulsions in the fairly distant past (70+ years ago) - Ron had talked about that on here with regard to stop baths etc.