Stop not buffer.



One of the most popular over the counter acid stops.
Made from citric acid with colour indicator.

Stop is the second part of the development process, but how many of us give it a second thought. Most of us when we come to developing our first film tend to do what the manufacturers, friends and teachers suggest without delving into what the relationship is between these elements in the process. There is nothing wrong with this approach we are all eager to get on and see those all important first images. With success, we continue settling in to a way of doing things that produce good results. It's not until we start printing that some faults with the negatives rear their heads. Dust and hair marks being the most common but then there are those odd black spots appearing in the skies here and there. This is when the controversy about how we stop the development process comes to the fore.

There are two main categories. The more aggressive with chemicals and the gentler water stop. The later is not a stop and it is misleading to call it such.   It dilutes the developer to the point where it no longer has an affect on the emulsion this can and does lead to unevenly developed negatives and I cannot understand why it is recommended (for film only) other than to increase the longevity of the fix, a buffer or as a way of creating a certain style to the negative. 

Have been processed using a citric acid stop.

I personally prefer the more aggressive chemical route, when the stop go's in, the developer is stopped in its tracks producing a clean crisp negative but you need to be careful.

A popular choice in the make up of developers is Sodium carbonate, an alkali. When this comes into contact with an acid based stop it produces carbon dioxide gas that leads to blistering of the more sensitive film emulsion,( not the case with enlarging papers). It manifests its self as a pinhole in the denser areas of the negative. There are ways around this by using developers that are formulated from mild alkalis either balanced or borax which do not produce the damaging over heating or gas when used with acid stops.

A reflection of St Pauls in London.
Processed and printed using all Ilford products

Stops are made from several different acids the most popular is acetic with a pH dye indicator. The others are citric and boric. You can also use a simple solution of sodium bisulfite. Be careful which stop you choose as some produce green staining with some enlarging papers. Another precaution is to use the stop bath at a lower working temperature to the developer; I know this is a controversial move but I have used this method for years without any of the problems suggested by others.

Processed print faults

Exhausted Developer

With all the processes that need to go well when producing a print in the darkroom it is surprising that faults are not more common. Even so the odd  one comes along to de-rail a good printing session. It does not matter how experienced you are sods law trips us all up!

Exhausred stop

Here are some of the most common faults: 

●         Chemical fingers - this where odd irregular marks appear on the finished print usually at the edges. Make sure your hands are free from chemical contamination and dry before you handle photographic paper.

●         Exhausted developer - fails to produced a full image once it has reached its completion time.

Exhausted Fix

●         Wrongly diluted developer - produces faint grainy image. A bit like the above.

●         Exhausted stop - leads to a purple tone to the white areas of the print.

●         Exhausted fix - the slow brownish toning of the finished print in day light.

Related Posts:

Enlarging len which aperture?

The quality of your enlarging lens will lead to better and sharper results at greater magnification. The aperture ( low number = large opening, high number = small opening) you set not only affects the amount of light it lets through but the depth of field as well. A good average aperture is F/5.6 in most cases. If the exposure times are to short a larger F number is needed, this will give you a chance to hold back shadow areas that may become to dark to show any detail. But don't get carried away and close down the lens by too  many F numbers as this may over heat the negative causing it to buckle, making the picture loose sharpness.

Stop bath

Does what is says on the bottle! It is used instead of a wash as it helps to prolong the life of the fix and stops the developing process straight away. You must be careful not to contaminate the developer with stop, it will destroy it.

Stop can be obtained in two types of concentrated solution. One is odorless made from citric acid and the other acetic acid with a vinegar smell which can be quite pungent if used for prolonged periods in the darkroom, when processing prints in trays. Both have a colour change indicator added to the solutions so you can tell when it is exhausted.

Dilute the concentrated Stop one part solution to nineteen parts water (or as instructed on the bottle.) say 50 mls stop to a litre of water with a process time of one to two minutes, you will not gain anything by extending the stop time it is most active in the first few seconds. Agitate for the first thirty seconds, this ensures the developer has been completely deactivated, then ten seconds in every minute if you stop for two minutes.

Wet side of the darkroom.

On this side of the room you will have laid out your developing dishes in the following order: developer, stop-bath, fix, print washer and/or sink. These may have heaters under them or you can have a slotty laid out in the same way. Obviously this will take up less space.

Typical wet side layout

This is where you keep your chemicals, it is also the place that the solutions are poured out and back into their storage containers. The height of this table needs to be right so you can work comfortably in the standing position. It is a good idea to store these chemicals under the table if there is a leak it will go on the floor and not drip into your working dishes ruining your prints. For safety reasons it is not a good idea to lean over your dishes to retrieve items from shelves above while your working as you may knock the contents of the dishes over yourself.

Remember that these chemicals need to be treated with care and you should follow the safety advice recommended by the manufacturer.