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Discussion in 'B&W: Film, Paper, Chemistry' started by Fellipe de Paula, Sep 10, 2009.
How strong to tap the bottom of the tank to free the air bubbles? Just a gently tap?
This is a good question, but really hard to answer over the internet.
I give it a good slow but firm rap on a cushioned surface - something like a countertop with a towel on top.
You don't want to break the tank!
I've even given it a tap on my left palm, it doesn't have to be slammed down on a concrete floor. Some people use the term "rap" even, I don't now what he big difference is but a gentle tap on a cushioned surface just like Matt says is exactly what I do.
I give it a good thump by bringing the SS tank down on the heel of my hand after the last tip over of each agitation cycle. I guess the hand is kind of going up to meet it. Not hard enough to hurt, though.
How do we know without opening the tank to look? Maybe an experiment with outdated or sacrificial film would be in order. I use such vigorous agitation that there sholud either be no bubbles or bubbles everywhere, But I still give it a good rap when I set the tank down.
Just look in the tank when you are doing your wash, or even photoflo rinse. Suffice to say I'm not 100% sold on tapping the tank. I've seen bubbles stick even when doing the photoflo rinse with distilled water. If they are sticking with THAT combination of liquids in the tank I highly doubt a few taps will get them loose during the development stages. Small bubbles have a tremendous amount of surface tension and a little tap will NOT make them go away.
I use the twirling stick to prevent additional air bubbles from forming and live with the comfort that every 25 seconds any bubbles on the flim will be relocated and should have minimal effect on development.
Ok: que the poster that will say he/she has been developing film since it was made from stone and developed in dinasaur urine to say I am wrong...
Actually, I found dinosaur urine makes a good stop bath.
Sorry, I couldn't resist.
Some of the kids in the darkroom where I work sound like they are driving nails at times - way too hard. Just about the same force as the tank would encounter if you dropped it from about 2mm height works for me (best estimate I can come up with in words )
Fill all the way to the top expells most of the air. the raps mentioned above should be sufficient. When you finally open the lid and find foam you will know there was air. If there are no bubble marks on the film your technique is okay.
About half the impact of rock-paper-sizzers.
The bubbles on the film form slowly. they form regardless of how full the tank is. If you rap right away the bubbles are too small to release. Time is needed to allow them to form, to be large enough to be dislodged by a sharp rap to the bottom.
My technique is to fill, light tap, agitate 30 sec. let rest 15 sec and then a sharp rap to the bare counter. I base this on a test I did long ago. I used a plastic reel with a glass beaker with various films in room light. Most film/dev combinations do not produce troublesome air bubbles. But the bubbles do not form instantly.
I found the best technique is to fill the tank and load the reels in the tank in the dark. The steps I use is load the reals as normal in the dark in an identical tank. Lights on, fill dev tank and get all ready. Lights out, open dry tank, move reels to dev, lid on, lights on. It's a PITA and I hardly ever do it but if you have a film that tends to have air bells it is a way to reduce them.
If the tank has been naughty, you give it a good spanking.
Not to strong I had a Paterson tank with 5 spirals spli tapping too hard
I did experiment last year & posted the photos on APUG, tank filled with a spiral/film water etc and the air bubbles were quite clearly visible, I'd been having some problems, but the water here is quite variable from a reservoir much of the year and a borehole in long dry spell, with a much higher salt content. A drop of dilute wetting agent solved my problem, but too much makes things worse.
I prewash my film with plain water and about half the amount of photoflo as normal. I've never had a problem with trapped air bubbles. You can also use a product called LFN wetting agent directly in the developer. Its the only brand that claims compatability with most developers. All that said, a gentle rap or three about like clapping your hands should sufice.
I confess that I rap my Jobo tank fairly hard. It looks fairly well constructed, so I haven't worried about cracking the tank. Maybe I should?
My suggestion is take a dry tank with its spirals, fill with water, and observe the air bubbles, then see what is best to dislodge them. Tht's how I found my best way to eliminate them.
Nah, I don't think so. I also have a Jobo tank and it's made of a plastic that doesn't seem "brittle". Compared to it, a Paterson tank that I also have feels much more crack prone.
Per Volquartz recommended that I buy a 5"x5" wood block cutting pad from an art store and give one or two sharp raps on that. I found that it does the job and cuts down on the noise too.
Well, now. That's basically the "test", isn't it?
If you find that you cracked the bottom of a plastic tank or dented the bottom of a stainless steel tank, you might not want to use that much force in the future. I thought you would like to know.
Jason Brunner has a great video on Youtube illustrating the proper knocking routine. My memory is you knock first on the side of the bottom like against the edge of a sink, and then knock a few times right on the corner before setting it straight down.
Since I'm usually developing film after midnight and until about 3 AM, I like the heavy rapping. It keeps my neighbors wondering
I use something like the handle end of a screw driver and rap the side of the tank, not very hard but with many repetitions. SS or plastic tank. Works for me.
This is the right approach with me.