Newbie Van Dyke questions

So I have my first batch of sensitizer ready (I think) but unfortunately the printing will have to wait 'til tomorrow. I have a few questions for those more experienced than I.

My house has mostly fluorescent lights, I don't like them but can't do much about it yet. Is it a no-no to keep the brown glass bottles around them?

I split the 100ml solution in to two 50ml bottles, the largest size the pharmacy had. At the bottom of each bottle is a decent layer of something that looks like light sand or coarse sugar. Is this the precipitate I've heard forms or did I not mix the chemicals enough? Will giving the bottles a good shake get rid of it, and should I do that before coating anyways?

Lastly, the only special warnings that came with the chemicals beyond the usual don't drink it, don't splash it, if you get it on you wash it off quick applied to the potassium dichromate and silver nitrate. I haven't mixed the dichromate yet, but the AgNO3 is part of the sensitizer. Anything special I should do when handling the sensitizer? If I get it on me, I'd presume it would turn my skin brown or black in short order so that I would know I got it on me. Is this so? Lastly, should I wear gloves when coating in addition to the mixing?

Thanks a lot for your help!

- Justin

Justin,

No need to worry about the solution in the brown bottles being too close to fluorescent lights.

I'm not sure what van Dyke formula you are using. The one I've used actually is stored as three separate solutions (silver nitrate, ferric ammonium citrate and tartaric acid) which are mixed just before coating paper. I don't recall any need for dichromate. And I don't recall a precipitate in any of the solutions.

As for handling and coating, wearing gloves would be an excellent idea. You want to have no/minimal direct exposure to the chemicals.

- Paul

My solution didn't have crystals at the bottom but it did suddenly go sort of curdled milk looking, i gently (50C) warmed the bottle up and let it sit longer and it had mostly gone into solution by the time I got around to coating today and it apparently didn't give me any problems (though it does slightly settle out if left for a while). Yes wear gloves, I always wear gloves for all photography chemical handling. It's better to be safe than sorry and really you don't need tactile contact with these things anyway. I also wore full goggles as I was concerned if there was any splashing or anything, nothing would get into my eyes then.

I believe that most people keep the sensitizer as one solution. In school we kept them in three separate bottles, but I don't think that's really necessary.
The sediment issue seems to be quite typical. I give my new bottle of solution the odd shake over at least a 24 hour period before using. Strain the remaining sediment out (after giving it a shake) using a coffee filter. it shouldn't come back after that.
the potassium dichromate has been said by some to offer contrast control; this has been found out to be false. It's also pretty wicked stuff, so I would avoid it.
Yes, your skin will turn brownish black from the silver. you don't want to get silver on your skin. it's quite bad for you. I've gotten a few spots over the years and they fade after a week or so.

My question is: do most people refrigerate their sensitizer immediately after mixing or wait till later after straining? I'm wondering if the cold of the fridge might increase the sediment accumulation?

-david

Oh I should also add: always add the silver last and very slowly as your mixing. This might explain the curdled milk look heather. I know even as I add the silver part of the solution it has that appearance.

-david

Hmm, I did add the silver rather quickly as I was concerned about it dripping on to my work table. Looking at the sediment again it doesn't look crystal like, it looks almost fluffy... odd. I had purchased a Photographer's Formulary kit and was just following their instructions. I bought a box of vinyl medical examination gloves, any problem interactions with the chemistry? I was hoping to get the ones that are common for nurses to wear now, the ones that come in the same colours as scrubs (I think they're called nitrile) but we did not have any. I have the sensitizer sitting in a hot water bath and will shake it periodically to try and get that sediment to dissolve. I'll keep you all posted on my progress!

- Justin

Edit: After sitting in the heating bath for a bit and a vigorous shake the sediment seems to have dissolved. We'll see in the morning how it looks and hopefully our new spring weather will give me a few more hours of sunshine after work tomorrow!

I had the same problem as I've read elsewhere on APUG... I was adding the silver nitrate slowly drip by drip, no problems, got down the last 1-2ml and it suddenly went curdled milk all at once. Apparently adding some more tartaric acid will help it go back into solution but I didn't do that.

I think the mixed solution gets better with age, as in several months to a year or two old. I would not store the chemistry separately. And yes, a bit more tartaric acid helps he silver go back into solution.

Joe

I've been doing some printing today and I seem to be getting the hang of it. One thing that's bugging me is the time to coat a sheet, let it dry, add the second coat, let it dry, and THEN make the exposure. Would VDB paper be OK to pre coat at least a few hours in advance, or even a day or too? I've heard this does not work well with some other alt processes.

- Justin

I usually do enough paper for a printing session first, usually about 4 sheets. I leave the paper hanging in the humified room until I need it.
I used to do it the night before. However, when I started humidifying the paper, that became difficult. Apparently, you are supposed to keep the paper at around a 60% humidity until it goes into the light box.
Thought, doing it the night before seemed to be fine. It just looses dmax over time. I'm not sure how old the paper has to be before you start to notice? I wouldn't go more than 24 hours myself.

-david