To buffer or not
I'm beefing up D23 with lye to make it more active when developing reversals. I've seen many recipes that use borax as a buffer.
My understanding is the buffer is used to keep the PH stable for longevity. I plan to only use this as a one shot and I am not sure how much, if any, I would need to use.
The degree of buffering can also have an effect on tonality (the shape of the characteristic curve) particularly in areas of high exposure when developing a negative.
So the action can be considered localized on the surface?
I'm not very knowledgeable regarding the ins and outs of reversal processing, but just wanted to make the point that in negative development, buffering is more complex than just storage longevity.
Generally speaking, poor/weak buffering is a characteristic which can contribute to "compensating" or lower contrast development because as acidic development by-products build up in areas where lots of development is taking place, the local pH on the surface and/or within the emulsion can drop, leading to lower activity.
The difference with reversal 1st stage developing vs negative developing, is reversal requires much greater density build up. The more you have, the less solvent you need. The solvent is usually counter productive on quality when compared to a comparably developed image without.
I have just mixed up a concoction, based on D23 with the following ingredients added in order
dist water 700ml
pinch of Sodium Sulphite - assist the dissolving of Metol
Metol 7.5g - strait from d23 recipe
Sodium Sulphite 50g - d23 amount halfed. I am not looking for lower grain, as this grain that is developed get's removed. It does not really effect the final image
Potassium Bromide 5g - I have seen these higher amounts in other reversal formulas, and I have had problems with some films fogging too much
Borax 5 g - this is a shot in the dark, but likely needs more.
lye 10g - tested to give a ph of 12
dist water to make 1l
A quick dunk of a room exposed leader develops to pitch black in 30 seconds, noticeably in 5 seconds. (orwo n74+)
With this level of activity, I'm guessing I'm probably off on the level of buffer I need.
A good buffering system is really only required for replenished developers. With these developers it is important to maintain activity at a constant level over a long period of time. For single use developers buffering is less important. in fact acutance developers such as the Beutler formula are poorly buffered by design. In addition the first bath of a two bath developer need not be buffered at all.
Thanks Gerry. Any insight is helpful. Chemistry class 30 years ago is not much of a guide. ;) Would removing the borax completely be ok?
I did a dry run this afternoon and I was surprised at my result. I inspected after the bleach and clear steps and discovered half the emulsion was gone. It was if I had used a lot of solvent. The next run with 1:1, gave a almost perfect positive which I was only able to achieve with a 1:1 with dektol and a solvent. This tells me 1) I have the activity I wanted and 2) I have a big fogging problem. The bleach must of removed all the fogged emulsion on the first try.
After looking around the net, it looks like if I double the lye, remove the borax, add some more bromide and add some solvent, I will have D94 without hydroquineone. There is nothing like re-inventing the wheel....;)
You really shouldn't have to use lye (sodium hydroxide) as it will make the emulsion too soft and delicate and easily damaged. You could add sodium metaborate (Kodalk) or sodium carbonate instead. A paper developer like Dektol which has hydroquinone in it will also increase contrast. Have you looked at Ilford's instructions for reversal processing? http://www.ilfordphoto.com/applications/page.asp?n=90
I have been reversal processing for a few years and have made it around the block two or three times by now. I have devoured virtually everything that was out there, good and bad. I do keep looking....
I didn't know that lye did that. However I do have a few pounds of Kodalk, but it doesn't go much above ph 10. I really needed 11-12. Sodium carbonate I have is not that fresh and there seems to be some hydration with it. Measurements with other recipes seemed to be off. I guess I could just add until I got the ph I needed, or get some fresh... ;)
Dektol was adequate but I do have a few problems. The first is 4l of the stuff get's a little rank by the time I get to the end of it and the smaller packs are a blatant rip-off. I've been trying to focus on something I can make (I make everything else I use) so I can make how much I need and when I need it.
I live in Canada and it seems like I will have to wait for the second coming before I can get someone to sell me hydroquineone up here. It's amazing how much of it is around; look but can't touch. I have ascorbic acid, but have only a few grams left.