Uneven Negative Density

<p>So, I develop black and white film, and every once and a while I notice that my negatives, when scanned have an uneven exposure. <br>

The unevenness is usually around the edge of the film. It usually happens when the the picture is very high key, but not over exposed.<br>

Could this be my agitation technique, or my tank? I use a plastic Vivitar tank from the 70's or 80's (inherited the thing, no idea how old it is), agitation is done with this skewer type deal, and not by inversion.<br>

When I develop, all of my chemicals are at room temp, along with the water I use to stop, and rinse. But sometimes, I run out of rinse water, and I use the tap. My plumbing is crap, so when I try to get a stable temp with the faucet, sometimes short bursts of hot or cold water come out of the sink. Could this be the problem?</p><div></div>

<p>That effect is due to turbulence around the edges of the film, caused by the liquid flowing over the edge of the reels, resulting in increased development. I would suggest you go for inversion agitation: I give six inversions in the first 30 seconds, then one inversion every 30 seconds after that. Just before each inversion, I give the tank a swift half-turn as it stands on the bench, to impart some circular motion to the developer.</p>

<p>It's not so much a problem with the fact that you're uisng the paddle for agitation. I use it all the time in Paterson and similar tanks and don't have that problem. I did see this sort of thing happening when agitation was not vigorous enough. Developer around the edges of the film gets changed out faster than developer near the center. Inversion agitation usually takes care of the problem. If you are disinclined to replace your developing tank, try agitating more vigorously with the paddle. Constant agitation for the first 30 seconds followed by 5 seconds each 1/2 minute will do. Aim for a rate of 4 or 5 complete back and forth cycles in 5 seconds. That should do it. If it doesn't, then I'd look to replace the whole thing with a Paterson tank and reel system.</p>

<p>Thanks for the responses.<br>

With this particular roll, I decided that I would only do 2-3 agitations per 5 seconds every 30 seconds, rather than my normal regiment of 5 agitations for 5 seconds every 30.<br>

This sort of uneven development also happens when I use Diafine, rather than a normal single bath developer.<br>

I've been wanting to get a metal tank and reel for a while, so I guess this is my excuse for getting one.</p>

 

<p >My agitation technique is continuous for the first 30 seconds followed by 5 seconds agitation every 30 seconds thereafter. </p>

<p >A side bar: The binder used to hold the silver crystals to the film base is gelatin. No successful replacement has ever been found. Previously egg whites were used. Gelatin is ideal, as it is flexible, transparent, and insoluble given the time the film is wet. Further, it swells when wet. As it swells, it permits solutions to percolate in and out. Most times, you will hardly notice the effect of insufficient agitation. It shows up mostly when the subject is mundane. Its effect is worsened by short developing times. </p>

<p >A dot or period in the edge printing text is helpful to diagnose this problem . If the film sits in a stagnate developer, the fluid is absorbed however it remain as the site too long without being flushed out. In areas that have received high exposure the developer works and quickly exhausts. This means that area will not develop to completion. Sites not highly exposed are not too badly affected. Even if stagnant, the developer eventually trickles out because a spent developer is heavier than its surrounds. Once it exits, it falls slowly and this causes ebb currents. Fresh developer is drawn in but it is too late.</p>

<p >The spent developer blocks fresh from contacting the film directly below the well exposed site. The visible result , reduced density at the site. Below the site, the film will have slightly lowered density. The pattern seen is a comma like tail extending downward from the dot or period commonly included in the edge printing. This effect is named bromide drag. </p>

<p >Incidentally bromide a constituent of the sliver salt. It is liberated when the developer reduces the exposed silver crystal. Bromide is a necessary constituent of the developer formula. This is the restrainer that allows the developer to recognize exposed vs. unexposed silver crystals. As the developer ages (used) more and more bromide will be liberated. Soon the developer poops out. A developer replenisher can be used to regenerate it as this formula contains little or no bromide. The addition of a replenisher bolsters the spent developer and lowers the bromine count back to normal. </p>

<p>John,<br>

I have had good luck using the plastic tanks by sliding the tank back and forth on the table top about a foot, turning the tank a quarter turn each time. I use as much force as possible without the developer spilling out the drain holes. This seems to agitate more evenly than the spinner. However, I have gone to metal tanks for inversion agitation, which is fool proof.</p>

<p>Thanks for the advice Chris,<br>

I will try the table technique with my next roll.</p>