Kodak Indicator Stop Bath failure?

[MikeS]

Hi All.

A couple of days ago I mixed up 5 liters of Kodak Indicator Stop Bath (I have 5 liter bottles). Today I went to use some, and when I poured it out it was clear! I was surprised to see this, and it also didn't smell like stop bath, but rather sort of like the smell of a box of bandaids. I tested the pH of the stop bath, and it was still acidic (I used a swimming pool tester, so I don't know the exact pH), I then tried pouring some developer into it to see if it would turn purple, and it didn't. Is it possible that the indicator has gone bad? I've never seen this before!

I mixed up this stop bath with tap water rather than distilled water as I was running low, and figured it didn't matter to stop bath, my local water is slightly alkaline, but the stop bath was the proper color yellow when I first mixed it.

Can anyone tell me what's going on?

-Mike

 

[dr bob]

I've never heard of such. It is almost impossible for acidic acid to "go bad" as it is already as bad as it can get (the final stage in oxidation of ethyl alcohol)

The indicator is a stable dye so I think that is not a possibility either. Acidic acid in stop is so concentrated nothing I can think of in your tap water could possibly overcome it. That leaves only one possibility in my thoughts: maybe you had the wrong bottle. I sometimes think my developer(s) solutions smell vaguely like "band-aids".

 

[Neal]

Dear Mike,

I would like to second the "wrong bottle" possiblility. On one occasion I used Dektol instead of stop bath when developing a roll of film (I had clearly marked the bottle, I have no excuse<g>). There are lots of similar stories wandering around the various photography forums.

I will keep my even more embarrassing gaffs to myself. ;>)

Neal Wydra

 

[David Brown]

I would like to second the "wrong bottle" possiblility.

A second "second".

Mix up some new stop bath. Poor a little of the bad stop into it. 50 cents says it turns purple.

Cheers

David

 

[fhovie]

It is almost impossible for acidic acid to "go bad" as it is already as bad as it can get

My thoughts exactly

 

[MikeS]

A second "second".

Mix up some new stop bath. Poor a little of the bad stop into it. 50 cents says it turns purple.

Cheers

David

David:

Well, 50 cents would be wrong! This is not a case of wrong bottle, or wrong chemical in bottle. Stop Bath is one of the few Kodak chemicals left that I still use, and it's odor is very distinctive, I don't think I would mistake it anywhere. But, as you suggested, I mixed up some new stop after pouring most of the old down the drain (I saved some to try adding the new stuff to) Mixed up the new stuff, and it too was nice and yellow like it's supposed to be (and like the original batch was originally), added some of it to the old stuff, and it just turned slightly yellow.

I'm not saying I'm above mixing up the wrong chemicals, I've done it a couple of times in the past (I found out that when you use fix first the film comes out extremely underexposed ) but Stop Bath is not one of the chemicals I would confuse.

It's going to be interesting to see if this batch also turns clear within a couple of days!

-Mike

 

[David Brown]

Well, 50 cents would be wrong!
-Mike

Sorry. I owe you 50 cents.

Can't imagine what happened. Fortunately, stop bath is cheap!

 

[MikeS]

It's doing it again!!

well, now it's getting weird. I mixed up a second batch of stop bath, and within a few minutes it's already starting to turn clear! A friend here suggested that perhaps because I'm using a water storage type bottle (I got it a Walmart, it's got a spout on the bottom, and they stack real nice next to each other) that perhaps it's not acid resistant, and after using it for more than a year to hold stop bath perhaps the rubber seal is breaking down and effecting the stop bath. I've just mixed up a liter of stop bath in a separate container, and I'm waiting to see if it too turns clear. If so, then it's got me really nervous about what chemicals are in my local water

-Mike

 

[ras351]

Hi Mike,

Not sure what indicator Kodak uses but I've found the Ilford odourless stopbath does lose some of the yellow colour before it changes to purple. I tend to toss it when it gets to this stage. One thing you can try is a poor persons titration to find out if the potentially contaminated stop has had its pH changed. Basically you pour a fixed amount of fresh stop mixed in a glass container into a beaker (or some other glass container) and add an alkaline solution (you can use developer or a sodium bicarbonate solution) noting how much is required before the indicator changes colour. Make sure you swish the solution around to ensure it's properly mixed. Then do the same thing for the possibly contaminated stop using the exact same alkaline solution and the same amount of stop as in your first test. This should tell you if your contaminated stop is less acidic than a fresh solution. If you were pedantic and had access to a chemical lab you could take it further but it'd be easier to distill/filter the water and buy a different storage container.

Roger.

 

[ann]

i have been following this with some interest and can't really add to those above, but i just can't help asking; why pre-mix the stop bath?

 

[MikeS]

why pre-mix the stop bath?

The main reason is it's easy. I've been premixing stop bath for a few years, and it's just easier than mixing from concentrate each time, not to mention that the smell of the concentrate is kind of strong.

As a further test I mixed up a liter in a separate container, and while it's still slightly yellowish, it's definitely less yellow than it was when I mixed it up. So it appears that the problem is with my local water supply rather than my storage bottles. Wow, I knew that my local water was slightly alkaline, I just didn't know how bad it was! I wonder if there are other chemicals in the water that are causing this? Of course the quick fix for this is to mix up the stop bath using distilled water (which is exactly what I'm going to do now) but I'm kind of curious what's in my local water!

-Mike

 

[ras351]

Hi Mike,

I'm curious as well to know what's in your water although I can't imagine it'd be too alkaline or it'd feel slimy and you'd end up with lots of people in hospital. Most acid/alkaline reactions are fairly quick (throw some bicarb into vinegar/acetic acid and you'll know what I mean) so there might be some kind of weird endothermic reaction going on which is breaking down the acid (or indicator). You could stick some in the fridge and see if that slows down the colour change. We really need a chemist as although I walk past chemistry labs nearly every day, apart from photography, I haven't done any real chemistry for 15 years.

Roger.

 

[photomc]

At this point, a call to Kodak might be helpful. Have not worked with their customer service in years, but at one time they were pretty helpfull. Also, there are places that will test water (and local water supplies are tested - that's how they get to put those little signs that say something like Superior Water Supply, etc - they should be able to give you a break down of what IS in the water). Keep us posted, as this is very interesting and NOT the norm.

 

[ann]

thanks for the reply,
ann

 

[titrisol]

Don;t worry that much about this, the indicator is becoming clear, which might as well be normal. The indicator is bromocresol purple, which changes color with pH as follow:
5.2 -> yellow
6.8 -> purple
If your water was alkaline it should have turned PURPLE, not clear.

I don;t believe the acid is gone bad, but maybe the indicator is being affected by something, so I'd try to see if the acid is bad or if the indicator is gone:
Put a teasppon of baking soda in a glass and add small qttys of your stop bath.
If the stop is good, it'll fizz and if the indicator is good it'll become dark

Depending on how you are diluting it you'll need some more or less to stop the fizzing.
But at 1+63 (kodak reccoemnded) there should be 1.35% acetic acid, so it should take about 250 ml of your solution to make 1 tsp of baking soda stop fizzzing
(5g of soda are neutralized by 3.57g of acetic acid)
If you diluted less then it should take proportionally less.

well, now it's getting weird. I mixed up a second batch of stop bath, and within a few minutes it's already starting to turn clear! A friend here suggested that perhaps because I'm using a water storage type bottle (I got it a Walmart, it's got a spout on the bottom, and they stack real nice next to each other) that perhaps it's not acid resistant, and after using it for more than a year to hold stop bath perhaps the rubber seal is breaking down and effecting the stop bath. I've just mixed up a liter of stop bath in a separate container, and I'm waiting to see if it too turns clear. If so, then it's got me really nervous about what chemicals are in my local water

-Mike

 

[kwmullet]

Perhaps a Kobayashi Maru is called for.

My suggestion would be to fill your stop tray with tap water each session, then add 1 teaspoon of citric acid for each liter of solution. Little or no smell. Lemonade has more of a smell. Very effective. If you do TONS of printing in one session, rub your fingers together in the solution and check to see if there's still a bite to it. If it starts to feel a bit slimy, then it's time to add a bit more citric acid.

As I got it, citric acid comes as a powder. I got it from my local organic grocer's bulk spice section for a few cents an ounce. I got two or three dollars worth, and it was more than I needed to last me until I switched to a completely alkaline tray line, at which point I didn't use a stop anymore.

There's lots of discussion of citric acid in the archives. (there was a url link here which no longer exists) is probably as good a place to start as any.

-KwM-