Acidification of Fabriano - a question

[seans]

I have been starting to print pd on Fabriano Artistico Extra White 140 lb hot press. I am going to print gum eventually so that is the reason for this paper choice.
I have been told that I need to acidify the paper and was given instructions to do so in 4% oxalic acid for 15 minutes. I was told I could do multiple sheets at one time as long as I rotate them.
I have been doing so - the printing is working - but when I first coat with pd I get a mottled appearance - looks almost like age spots - some darker spots that seem to take up more pd. I dont know if it is related but when I print a greyscale image not all the squares of the same level read the same on the print.
In other words - a 20% square may read 18% in one square but 25% in another 20% square.
I was wondering if some one could tell me that is the norm for this paper or am I doing something incorrect in my process
thank you
Sean

[Colin Graham]

Could it be the sizing has broken down in spots? I had the same mottled look with Arches Aquarelle when I held the sheets wet from the acid bath (5 minutes in 5% citric acid in my case) up to a light, and the emulsion really soaked in fast. I thought I had ruined the paper and was all set to resize, but they printed great.

[sklimek]

I have been told that I need to acidify the paper and was given instructions to do so in 4% oxalic acid for 15 minutes. I was told I could do multiple sheets at one time as long as I rotate them.

Hi Sean, I've printed quite a bit on Artistico for platinum and I'm thinking that maybe your oxalic soak is too long. You may want to try a 2% for only 2-4 minutes in about 70 - 80 degree water. I'm thinking you may have dissolved the surface size unevenly from your 15 minutes in the 4% and this may be causing your 'blotchiness' I do agree that constant agitation in the oxalic is a good thing. Also, when I insert the Artistico I have noticed the surface size (which is heavy for this paper because it was created for water color) shows a type of uneveness as it tries to absorb the solution. I slide it in and do a few 'hard' tray rocks before the next sheet goes in and rotate constantly.

Best - Stan

[Ben Altman]

Hi Stan

Do you wash after the oxalic, or just dry and coat?

Thanks, Ben

[sklimek]

Hi Ben, I just let it dry naturally and coat, the 2% primes the paper well. It’s good though to change out the oxalic from time to time; it works pretty hard de-buffering and breaking down the surface size. I usually mix a new gallon after about 20 11 X 14” pieces. After you tape down your paper for coating it’s a good thing to brush the paper well before laying down the emulsion – some of the crud you can’t see from the oxalic bath can adhere to paper fibers and show up as a black dot after exposing. I usually take a paper towel roll and drag it down the paper a few times as if it were a silkscreen squeegee.

Stan

[Ben Altman]

Thanks, Stan! I love the paper, but have not so far had a good m/o. I've moused around forums for info, but your method sounds like it's better worked-out than anything I found. This will save me some learning the hard way.

By the way, which side do you prefer? I've tried both.

Best, Ben

[sklimek]

Hey Ben, I prefer the back. The front has very thin parallel lines closely spaced together that can be seen upon close inspection with the finished print. The back has a nice random pattern that looks great.

BTW, Artistico responds well to induced humidity, you may want to try a sheet w/ no humidity and one w/ about 83% (for comparison) humidify about 15 minutes after coating before exposing, lay down a sheet of Mylar/plastic on your exposure bed to lock in the humidity during exposure – in other words, make a Mylar, print with negative and glass sheet of vacuum frame - sandwich, this will keep the humidity locked in for exposure.

Stan

[Ben Altman]

Hi Stan,

Yeah, I'd noticed those thin lines - I'm glad you are seeing them too, so it's not an artifact of my diginegs. I'm "between darkrooms" right now, the old one was temporary/improvised and had little humidity control, so I was humidifying the paper before coating. I'd noticed some pretty radical color effects which I had assumed were humidity variations. (I'm using POP Pd/Pt.) Should be fun to explore once I get up and running again - maybe there's a way to vary the look of different parts of the print... Thanks for sharing your expertise!

Ben

[sklimek]

I'm "between darkrooms" right now, the old one was temporary/improvised and had little humidity control, so I was humidifying the paper before coating.

Just a thought, it would probably be worth the time to try and control your darkroom humidity at around 25 - 35% and make a humidity box for your induced humidity. This kind of standardization really pays off for control in predictability and you won't feel like your in a sweatbox!!!

Best - Stan

[Ben Altman]

Good idea, thanks!