How Hard Should You 'Tap' Canister When Processing Film?

DF · Oct 19, 2020

How hard, and also how many taps? I've always been skeptical as to if this really does disperse/remove air bubbles, or if there's any point in it at all. In fact, I wonder if it has a disruptive effect in some way on the film running alongside the reels, if too hard tapping increases contrast for instance. There's this guy who after inversions - doesn't tap, instead gives one hard wack.

MattKing · Oct 19, 2020

I tap-whack - on a folded cloth.
Not hard enough to threaten the tank, but not too gentle either.

Donald Qualls · Oct 19, 2020

Air bubbles are buoyant. Each time you tap/bump/bang the developing tank, you're momentarily subjecting it to hundreds of times the acceleration of gravity, which multiplies the force on each tiny bubble by hundreds of times as well -- which is what causes the bubbles to move away from any place they've adhered due to surface tension.

Clearly, you don't want to bang the tank so hard to break it (if plastic) or dent it (if steel), but otherwise, two or three sharp raps is about the same as one massive whack -- but safer, if you use a plastic tank.

Any sort of agitation increases contrast in comparison to none, because it ensures there's fresh(er) developer available at the surface of the emulsion, where without agitation, there's an opportunity for the developer to exhaust locally where there's more exposed halide to develop. There are no significant difference in density in the liquids with in the tank, however, so banging the tank does not, of itself, increase agitation effectiveness -- something needs to cause the liquid to move around in the tank, relative to the emulsino surface, to do that. Swirling (like cognac in a snifter), twirling with the swizzle stick, inversion, rocking (substitutes for inversion in some tank types), sliding back and forth (Kodak's method for hanger tanks) -- something that actually makes the developer move.

pentaxuser · Oct 19, 2020

I always avoid tapping the tank if I am angry and turning green. Otherwise a couple of moderate but quite sharp taps of the plastic on a plastic surface seems to suffice

I did once employ a "tapper" as an assistant who was over enthusiastic. Thank goodness he eventually left the job to start on telegraph poles instead

pentaxuser

StepheKoontz · Oct 19, 2020

3 sharp taps for me, if you break or dent the tank, you did it too hard lol.

BrianShaw · Oct 19, 2020

3 taps from a height of 3/4 inch on a paper towel folded in quarters... using the tank weight to control force. Generally only twice in the first minute and no tapping during agitation thereafter.

chris77 · Oct 19, 2020

Do the twist, and you can forget about tapping..

chris77 · Oct 19, 2020

twirl, not twist of course

ProfessorC1983 · Oct 19, 2020

I always double-tap just to be sure.

Michel Hardy-Vallée · Oct 19, 2020

I never tapped, never had bubble issues. I like a good flick of the wrist when I agitate, so I suppose that counts for a tap.

Andrew O'Neill · Oct 19, 2020

Some of the tanks here have the foot worn completely away from over aggressive rapping. I could hear them banging their tanks on the counter from where I was sitting, in the ceramics room! It would make me cringe! Since I took over the photo program three years ago, I've been teaching my students to use the figure 8 agitation pattern. No bubbles. No need to rapping.

PFGS · Oct 19, 2020

I just smack my steel tanks with the heel of my hand a few times, never had a bubble problem & unlikely to damage the tank or pop the top off.

foc · Oct 19, 2020

I never tap just a good swirl at the start.

PFGS · Oct 19, 2020

Vaguely related question - why agitate at the start? The developer is fresh, why this prolonged agitation right up front? For me, usually a lot of that 30 seconds is taken up by filling the tank and I only get a few agitations in anyway.

Pentode · Oct 19, 2020

PFGS said:
I just smack my steel tanks with the heel of my hand a few times, never had a bubble problem & unlikely to damage the tank or pop the top off.

That's what I do, too. Two thuds on the bottom of the tank - metal or plastic - with the heel of my hand. Not hard enough to hurt.

BrianShaw · Oct 19, 2020

PFGS said:
Vaguely related question - why agitate at the start? The developer is fresh, why this prolonged agitation right up front? For me, usually a lot of that 30 seconds is taken up by filling the tank and I only get a few agitations in anyway.

For me that first agitation is mostly to get rid of any bubbles. I start timing after the developer etc is poured.

Alan9940 · Oct 19, 2020

PFGS said:
Vaguely related question - why agitate at the start? The developer is fresh, why this prolonged agitation right up front? For me, usually a lot of that 30 seconds is taken up by filling the tank and I only get a few agitations in anyway.

The initial agitation helps to start even development and removes quite a bit of the anti-halation dye, if you don't pre-wash. What kind of tank are you using that takes nearly 30 secs to fill? I use 1L tanks, both stainless and Paterson, and can fill completely in 10 - 15 secs. You may want to think about starting the timer once the tank is filled; many folks do this. The procedure really isn't critical as long as you're consistent. Doing a pre-wash step will mitigate the need to worry so much about fill time because it takes the developer longer to seep into the emulsion.

Regarding tapping... I give a medium smack on the side of the tank once I set it down after an agitation cycle. Never had air bells.

Donald Qualls · Oct 19, 2020

PFGS said:
Vaguely related question - why agitate at the start? The developer is fresh, why this prolonged agitation right up front? For me, usually a lot of that 30 seconds is taken up by filling the tank and I only get a few agitations in anyway.

BrianShaw said:
For me that first agitation is mostly to get rid of any bubbles. I start timing after the developer etc is poured.

That agitation (first full minute or first 30 seconds, depending who taught you) is mainly to ensure the film is thoroughly and evenly wetted as early as possible after the developer goes in -- this helps avoid unevenness, surge marks, hesitation marks, and similar issues.

Speaking of which, if you have a tank that takes you most of thirty seconds to fill, get rid of it (or at least put it on the shelf) and get a Paterson. Pouring from a graduate (pitcher), I can fill a Paterson in under ten seconds, have the inversion cap on, timer started, and be agitating in fifteen. Then, at the end, I can pour out and shake the tank (to minimize carry-over) in about the same time. If your tank takes most of 30 seconds to fill, it'll take similar time to drain, and during the drain step, before and as you pour stop bath, you have developer on the emulsion oxidizing from high-area, low-volume contact with air in the tank; this can lead to staining with B&W, and odd color artifacts with color (because it's oxidation products that make the dyes).

Vaughn · Oct 19, 2020

Our students were taught by the profs to whack the SS tank of the counter a couple times. I had to replace the counter once...even after putting out rubber pads to thump on. I thump on the heel of my hand a couple good times (SS tanks holding two 120 reels).

PFGS · Oct 19, 2020

Alan9940 said:
What kind of tank are you using that takes nearly 30 secs to fill?

Donald Qualls said:
Speaking of which, if you have a tank that takes you most of thirty seconds to fill, get rid of it (or at least put it on the shelf) and get a Paterson.

It's my one liter steel Kindermann with plastic lid & Hewes steel reels. It was already old when I got it in my very first load of yard sale darkroom junk 20 years ago and I've been using it (and the same lid on its 500ml brother) ever since, never once had any unevenness, staining, air bells, mis-loaded reel issues, tide lines, etc. It takes me about 20 seconds to fill because I pour in the developer with absolute neatness, not a droplet anywhere on the lid or outside the tank or on the counter or my hands, just a slow steady pour with the tank held at 45 degrees. Standardized early on on the sequence start timer - pour in - agitate - timer runs out - pour out, on the grounds that either way is arbitrary and best to be consistent. My exposure and dev time choices, and former excessive switching from one developer to the other, have been the only development-related issues I've ever had. I do avoid short dev times so maybe that helps.

I did try a Patterson once, hated loading the reels and the whole process was a big leaky mess, never again.

At least my hand-thumps are Photrio approved!

MattKing · Oct 19, 2020

With respect to development, arguably, the initial agitation is at least as important as all the rest combined.
It is what ensures an even start to the development. I agitate continuously for the first 30 seconds.

Donald Qualls · Oct 19, 2020

PFGS said:
I did try a Patterson once, hated loading the reels and the whole process was a big leaky mess, never again.

I guess we'll have to agree to disagree. I've completely quit using my stainless tanks; once I'm sure I've found all of them, I'll probably put them up for sale. I can load a 35mm stainless reel without problems, as long as I have a counter top to roll it on (can NOT load one in a bag in under fifteen minutes, though, and 120 is much harder) -- but I've been completely spoiled by being able to pour into the Paterson funnel and be done in seconds. For me, the plastic reels with the little ratchet balls are far easier (as long as they're clean and dry). Just a couple hours ago, I loaded a roll of 35mm into a Paterson reel while my biscuits were in the oven (9 minutes) -- and including adjusting the towel under the door (have to do that every time I go dark), opening the factory cassette with a bottle opener, and cutting both ends of the film in the dark, I had more than two minutes left on the timer when I came out of the darkroom.

Even my fast-fill Nikor tank takes way too long to fill. And if you give the Paterson inversion cap a Tupperware-approved "burp" after closing, it won't leak. I usually have to wipe up a little liquid off my counter after processing, but that's not due to the cap leaking; that's because I fill my pre-wet and wash under the sink tap and the tank gets wet when I do so.

markjwyatt · Oct 19, 2020

You have to do it hardly.

grat · Oct 19, 2020

I set mine down firmly enough on the sacrificial dish towel to hear a muffled thump, and then lightly thwack the side of the plastic tank twice for luck.

I have absolutely no idea if it's a waste of time or not, but since it doesn't seem to hurt... why not?

Sirius Glass · Oct 19, 2020

I bought a 3/8" thick block of linoleum that I use to give the stainless steel tank several hard thumps after I fill it with developer. Each chemical including water gets a hard thump. I have never in over 60 years had air bell problems when I develop film in a stainless steel tank.

How Hard Should You 'Tap' Canister When Processing Film?

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