The paper appears to be fine. I've used this paper for intaglio printing where the paper was soaked for even longer. Probably a 30 minute soaking would suffice as long as it is evenly soaked.
I like the colour of the print in the 1% solution bath. Cool with a hint of warmth. If I want a cooler tone, I'll soak the paper in a 5% solution.
AFAIK, concentration muriatic acid from hardware stores is something around 30-32%. 37% is "concentrated/saturated" HCl solution. In any case, both will fume. But there are enough diluted HCl products around -> calcium remover, toilet bowl cleaner and such (usually around 10%). I'm talking about these kinds of products not concentrated/fuming HCl... I totally agree with you about concentrated HCl. Why you insist that I'm suggesting concentrated whereas I clearly stated "diluted/non-fuming" before, I don't understand.
Anyway, acetic acid (or white vinegar) also can be used. (As I also said before...) Enigmatically, I had no comments about acetic acid but only about concentrated HCl - which I haven't suggested at all...
Could be that the practical consequences of using oxalic or HCl/acetic seems to be the same (which wasn't the case for me) but I still think diluted HCl or acetic acid is the way.
Oxalic acid will definitely leave neutralization products in the paper which may or may not affect results in the short term. (On the contrary I remember someone talking about the different results they were getting depending on oxalic acid strength; colder/warmer results when everything is the same in the rest of the process...) In any case, with pt/pd printing it's better to have a purer surface (= a surface with no alien content) to print on - instead of having paper that incorporates useless neutralization remains "which we know nothing about their future influence on the print's health". And that's a very good point to me since someone doing pt/pd is surely interested / concerned about the future of their prints...
FWIW on cost; A 7lb pail of Oxalic is ~$22 here. A case of 12 bottles of 10% HCL toilet bowl cleaner is ~$40. The oxalic makes ~16 gallons of a 5% solution the toilet bowl cleaner 6 gallons. The toilet bowl cleaner is ~5 times as expensive.
actually I am interested in acetic acid. I happen to have an old 80% solution which I used as a stop bath for silver (before I quit using it for its awful smell). How low do you think I have to dilute that, and how long can I leave a Fabriano sheet in it?
I use 5% strength (v/v) of 35% HCl (makes something like ~0.57M concentration if I'm not mistaking) for 4 minutes (agitating constantly and changing side facing the solution halfway), this is perfectly enough for printing good cyanotypes. (Which is a process that is very vulnerable to presence of alkali.) The bubbling and fizzing stops completely at about 3:30 or so. If you double the strenght (10% v/v) then 2 minutes processing is enough (tested), I just use a milder concentration to be more gentle to the paper, even if I haven't noticed any (short-term) adverse effect of using the stronger variant. 2 litres of the above solutions are enough to process an area equivalent to 5 full sheets of 22x30" sized paper (maybe more, but I haven't processed larger batches), it doesn't seem to slow down and loose strenght when used up to the previously stated capacity.
You can try to mix an acetic acid solution with a concentration something like ~0.6M to 1M and try several processing times (1, 2, 4 minutes and such). A good indication of enough processing would be the extinction of bubbling and fizzing...
5% HCl (v/v, 35% stock) doesn't smell offensive and is pretty safe to handle. (Half the strenght of the acid in our stomachs!)
Thanks a lot!
Don't forget to thoroughly rinse/wash processed paper. You don't want acid in the paper for the subsequent stages...
A side note about HCl (not acetic acid) and pt/pd printing is that you also get rid of small metallic remains in the paper (causing black spots and streaks in the print), since being corrosive it will dissolve those too... A bonus!