Kodak indicator stop

[ymc226]

I looked at the Kodak site but couldn't find the information I needed.

This is a follow up to the water stop question I posted earlier.

With vinegar (acetic acid), it was recommended that a 1:4 part dilution resulted in a 1% solution which was adequate.

Is Kodak indicator stop acetic acid and does the recommended 2oz/gallon dilution result in a 1% solution?

I want to use a one shot stop solution (don't want to save the solution). Can I use a more dilute Kodak stop solution and still get adequate stopping power. I know this issue is controversial as most think a stop is necessary, some 3 water changes equivalent and a minority think a one time water bath is enough.

 

[MattKing]

From the label on the Kodak Indicator Stop bottle:

"Contains Acetic acid (64-19-7) (912 g/L)
...
Additional Components Include: Water (7732-18-5), Bromocresol purple (115-40-2)"

As per the instructions, the concentrate is to be diluted 1 part to 64 for a working strength solution.

I don't know how 912g/L diluted 1/64 translates to a percentage solution.

I too would really like to know whether a more dilute, one-shot solution is viable.

 

[Photo Engineer]

A 1 - 2 % solution of Acetic Acid is viable. I have used it for years.

PE

 

[MattKing]

A 1 - 2 % solution of Acetic Acid is viable. I have used it for years.

PE

PE:

But if one follows the dilution instructions for Kodak Indicator Stop Bath, does one end up with a 1% solution?

Or, if I read the information on the bottle correctly, does 912g/L diluted 1/64 result in a 1% solution of Acetic Acid?

Thanks

 

[Christopher Walrath]

Actually it works out to about 1.5% at 1:63 mixing ratio. 912g/L equates to 30.4 ounces per 32 fl oz if you multiply the g/L by 0.03338 listed in the back of the Amphoto Darkroom guide. This is about 95 percent. Multiplied by the decimal equivalent of 1/64 (0.016525) gets us to about 1.5%. Someone check my math.

 

[Vaughn]

Actually it works out to about 1.5% at 1:63 mixing ratio. 912g/L equates to 30.4 ounces per 32 fl oz if you multiply the g/L by 0.03338 listed in the back of the Amphoto Darkroom guide. This is about 95 percent. Multiplied by the decimal equivalent of 1/64 (0.016525) gets us to about 1.5%. Someone check my math.

But what is the percentage of Acetic acid that is in the concentrate -- can't figure out anything without that info first...

 

[MattKing]

But what is the percentage of Acetic acid that is in the concentrate -- can't figure out anything without that info first...

I think 912g/L does indicate how much acetic acid is in the concentrate.

 

[Vaughn]

Thanks, I totally missed that

...sometimes my brain hurts...

 

[hrst]

I want to use a one shot stop solution (don't want to save the solution). Can I use a more dilute Kodak stop solution and still get adequate stopping power. I know this issue is controversial as most think a stop is necessary, some 3 water changes equivalent and a minority think a one time water bath is enough.

First, if you don't reuse, you can use somewhat more dilute solution because you don't need so much buffering power but only the pH. Even a more dilute solution of acetic or citric acid has low enough pH, but with lower buffer capacity. If you go very low, then you might want to add a wash step afterwards. Then, this would be a hybrid of acid stop and water stop .

Then, I don't think "majority" thinks that stop bath is necessary. While this could only be evaluated by a large survey, I would more likely guess the previous thread was a very good example of social manipulation. Relatively small number of people used very strong wordings to support their (partially false) statements, and what resulted in, was a belief that it would be the opinion of "majority". On the other hand, all of the people who used water bath for themselves said that both work in a rational way, or didn't say that you must use water. This doesn't seem to make the same impression, which is sad. Strong and simple "opinions" win over understanding.

To demonstrate and prove this effect, I counted and grouped the posts in Water stop bath thread:

Use acid stop bath: 4
Use water stop bath: 8
No clear opinion, but maybe acid stop: 1
No clear opinion, but maybe water: 2
Have had problems with acid stop: 1
Have had problems with water: 0

So, do you still say that majority preferred acid stop? .

 

[Mike Wilde]

On the home brew front, I have a stock solution of Bromocresol purple that I add a drop or two of to dilute acetic acid when I am using an acid stop bath.

The dye indicator was a part of over 300 different chems I was gifted when a biochem company when into receivership. Gradually I am using up some of them as I find uses for them. Some (obscure acids etc.) just get reacted with NaOH and then neutralized and flushed out just ahead of when doing laundry when I can find no good use for them.

 

[Photo Engineer]

Kodak indicator Stop bath is such a mix of ingredients I would hesitate to give a percentage value but the accepted value is that at working strength it is between 1 and 2 per cent.

If you start with 10 ml of Glacial Acetic Acid diluted to 1 L with water, you have about 1%. If you use 20 ml diluted to 1 L you have about 2%. If you start with 5 ml of 28% Acetic Acid and dilute to 1 L, you have about a 1.4% solution. Any of these will work.

PE

 

[bblhed]

...

Use acid stop bath: 4
Use water stop bath: 8
No clear opinion, but maybe acid stop: 1
No clear opinion, but maybe water: 2
Have had problems with acid stop: 1
Have had problems with water: 0

You may have counted me, in the water users, but I stated that I do use water, but if I wanted a totally repeatable process I would use stop bath in distilled water.

Here again, for repeatable process it does not matter what the strength of the solution is, it does matter that you mix it the same every time, and you use the same times and agitation. You would only have to worry about the concentration if you wanted to change something, like if you wanted a lower Ph so you could shorten your stop bath time.