Dektol and exposure to light

[Puma]

When I store my working solution of Dektol does it need to protected from light? I'm aware that exposure to oxygen will cause it to lose its effectiveness but unsure if I need to shield it from a light source?

Thank you,

Puma

 

[Ian Grant]

You need to shield from daylight, on a darkroom shelf it's less important (provided there's no uncovered widow) or keep in a cupboard.

Ian

 

[Puma]

Thank you for your response.

-Puma

 

[yeknom02]

Ian, I've seen enough of your posts on APUG to know that you really know your stuff. Can you explain why it needs to be protected from light? I was under the impression that only the silver halide in the paper was light-sensitive.

 

[Nicholas Lindan]

Light can enable faster oxidation of the developing agent and it can destroy the agent by photolysis. Quinones (Hydroquinone and Catechol) are sensitive to UV.

Light will destroy most organic compounds given enough time - things bleach out and rot when left in the sun. It is the UV that does the damage. Developing agents are all organic reducers/anti-oxidants.

Developers are supplied in dark bottles because the bottles are stocked in shops where sunlight streams through the front plate glass window.

In a darkroom you can store the developer in clear containers. It makes no difference. There is no sunlight and it is pitch dark most of the time.

 

[Photo Engineer]

Of course this is no hard and fast rule. For example, HC110 is supplied in clear plastic bottles and sits on shelves in photo shops. The big bugaboo is really Oxygen in the air and Carbon Dioxide in the air.

PE

 

[vpwphoto]

Yep... same reason Sam Adams has the high six pack holders and dark brown bottles.

 

[Puma]

So interior tungsten and fluorescent light won't hurt them either?

My darkroom is in a bathroom, there's no window in that bathroom but there is only a heavy darkroom curtain and while no direct light shines in there I do leave the curtain open during the day to help with the chemical odors. I spend time in there with the lights on too with mixed light sources.

Thank you,

Puma

 

[Photo Engineer]

Our Kodak storage rooms were all lit by fluorescent or tungsten. We used clear glass bottles for most all chemistry. Look at packaged concentrates and see how many are brown.

There are those that might argue that the concentrates are very resistant to light, but in my experience, photolytic reactions are rather ignorant of concentration or solvent.

If its gonna go due to light its gonna go guys! If it isn't it doesn't, and there are all shades in between.

Air and CO2 do more damage IMHO.

PE

 

[Ian Grant]

An interesting point is that I can't remember buying any commercial developer in a dark bottle in about 25 years. Ilford use white plastic, Agfa white & translucent plastic, Kodak mid grey & translucent plastic, the days of the brown glass bottle are long over.

However few if any commercial liquid developers contain Metol, and one reason why Metol based developers are sold as powders is they are more susceptible to the effects of bright light.

So Puma asked about Dektol, Kodak sell two types, the old D72 MQ powder version and Liquid Dektol (AKA Polymax dev) a PQ variant using Dimezone instead of Metol. They have different keeping properties, once the powder version is made up as a concentrate.

If your mixing powder developers either from commercial packs or raw chemicals the choice of storage container is more critical than it's colour. Obviously brown bottles are fine but with plastics it's important to use high density types, easiest is re-used commercial developer bottles.

With the wrong plastics a developer may begin to oxidise within 3 months even in a full sealed bottle. I found that to my cost when I used small translucent plastic sample bottles to store film dev about 4 years ago, the plastic breathes over time allowing oxygen to pass through.

So choice of storage bottle and keeping out of direct sunlight, brightly lit sunlit room are important to extend shelf life.

Ian

 

[Nicholas Lindan]

HC110 is supplied in clear plastic bottles and sits on shelves in photo shops ...

Agreed, the whole brown bottle thing is probably more tradition than necessity.

When Kodak sold liquid Microdol, D-76, Dektol etc. they came in brown bottles.

But then so did S. Carbonate and P. Bromide, I doubt light is going to do anything to that pair. But brown glass wasn't unusual, chemical suppliers used brown bottles for most everything.

I keep developer in Nalgene bottles. As the developing agents 'de-oxidize' the air in the bottle it develops a pronounced pinch, air being 20% oxygen.

I don't see how CO2 fits into this, though - can you elaborate?

 

[hrst]

Clear bottles are better because you can evaluate the solution for discoloration or gunk by your eyes easily. Amber bottles are tradition and this tradition is keeping too well in internet legends. Beginners are almost always suggested to use amber glass bottles.

The only possible exception may be if your chemical storage has a window where large amounts of light barge in.

 

[Bob-D659]

I don't remember Kodak selling any liquid in a glass bottle that wasn't amber. I still have a small bottle of film cleaner from the 1970's that is in an amber glass bottle, I'm pretty sure that hexane isn't really light sensitive.

CO2 readily dissolves in water and makes it more acidic. Using pete plastic soda bottles keeps that stuff in or out as well, as a soda bottle is a pressure vessel and will hold 75psi to keep the soda fizzy.

 

[hpulley]

I always heard it was the clear glass itself that could have problems, the additives to make the glass clear were bad compared to the brown glass but that could be a myth too... I have one of my father's old brown glass darkroom bottles but modern stuff is all plastic. Mine is mostly brown just because I don't want it to be confused with a food container after my daughter once told me my Ilfostop indicator stop bath looked like orange juice.

 

[Ian Grant]

That's another old wives tale, clear glass has been used for food, milk etc for years

Ian

 

[hpulley]

Thought so... no real reason to use glass now, just a chance of breaking it IMO.

 

[Photo Engineer]

Clear glass is the norm. You add things to make glass colored (in general - depending on the "sand" used) .

As for CO2 affecting developers, the atmosphere contains about 388 ppm. This may seem low, but the developer will eat it up and the pH will go down and as you keep using your developer, more CO2 diffuses into the container and dissolves in water. It is far more soluble in water than Oxygen and is therefore taken up more rapidly by the alkaline developer. In fact, when you use distilled water, the pH is about 6 instead of 7 due to predissolved CO2.

PE

 

[hpulley]

I've stopped bothering to use distilled water. I find with Ilfotol/Photoflo the final rinse doesn't make any difference and my developer, stop and fix seem fine diluted in tap water as well.

 

[Photo Engineer]

All commercial Kodak products assume that tap water will be used.

PE