Here is an example of a developer which contains all three of those constituents.
http://www.tetenal.com/sidaopener_uk.ht ... 100152.pdf
Moderator: Keith Tapscott.
MQ or PQ developers are good; in some cases MPQ are better. It's all in the wrist.Keith Tapscott. wrote:Here is a question for you to ponder over. Most B&W developers contain Hydroquinone with either Metol or Phenidone or a Phenidone derivative. Both Metol and Phenidone are super-additive with Hydroquinone, so why add both of them in the same developer formula?![]()
Here is an example of a developer which contains all three of those constituents.
http://www.tetenal.com/sidaopener_uk.ht ... 100152.pdf
As far as I know Murray, you are correct that the function of hydroquinone in a low to moderate pH developer, is to help regenerate metol or phenidone, although metol will work and keep fairly well as the sole developing agent, unlike phenidone, which is very short lived.Murray Kelly wrote:My understanding is (and someone will correct me if I'm wrong!!)but at a suitably low pH the hydroquinone doesn't do much except regenerate the metol or phenidone. If the carbonate is dilute enough the pH won't be high enough for the HQ do do any actual developing of itself.
Murray
I do know that Geoffrey Crawley uses both phenidone and metol in many of his 'FX' formulas. There are perhaps reasons that are not always clear why a given combination will work 'better' than another; it just 'does'. It's all trial and error.Lowell Huff wrote:Guys,
you are mis-informed about the relationship of the accelerators, Metol & Phenidone, and HQ. In the development process, Metol forms a salt with HQ and becomes ineffective. P acts as a catylist with the HQ to develop the exposed silver and then " searches for the next free HQ molecule", to continue the process until there is no more available HQ. This is the explanation of why MQ developers run "right up to the edge of the cliff and drop in the ocean." PQ developers " gradually slide into the ocean." The real differences and advantages of PQ over MQ are P is about 25 times more active than M, P is much less allergenic than M, P is much more resistant to high temperature (therefore we use it in machine process developers), P can be easily replenished, changing dilutition of a PQ developer will change contrast, and each form of P will change the standard curve to increase number of steps over M.
The advantage of a developer combining both is "bolstered syntax".
Well these are published free formulas, so they're not making him any money...they're just formulas he came up with, so there's no reason to suppose that they are more complicated than necessary. He has developed these formulas after lots of research into improving acutance while maintaining fine grain and good tonal qualities. They are very good formulas, and I have tried several of them. If he thinks that PMQ formulas are better I'm sure he has his reasons. Some of his are PQ only, some have glycin also.Lowell Huff wrote:I cannot attribute any advantage to FX formulas using both P & M, other than marketing differentiation. Just as with the proclaimed "advantage" of "alkaline fixer over acid fixer", it cannot be supported with science. It is only OPINION.
Lowell, I acknowledge that P.Q formulae are the most commonly available developers these days and for good reasons.Lowell Huff wrote:Guys,
you are mis-informed about the relationship of the accelerators, Metol & Phenidone, and HQ. In the development process, Metol forms a salt with HQ and becomes ineffective. P acts as a catylist with the HQ to develop the exposed silver and then " searches for the next free HQ molecule", to continue the process until there is no more available HQ. This is the explanation of why MQ developers run "right up to the edge of the cliff and drop in the ocean." PQ developers " gradually slide into the ocean." The real differences and advantages of PQ over MQ are P is about 25 times more active than M, P is much less allergenic than M, P is much more resistant to high temperature (therefore we use it in machine process developers), P can be easily replenished, changing dilutition of a PQ developer will change contrast, and each form of P will change the standard curve to increase number of steps over M.
The advantage of a developer combining both is "bolstered syntax".
In the last few months, I have tried Ilford DDX and Tetenal Ultrafin-Plus which are modern P.Q (Dimezone-S) developers and both are very good products.Lowell Huff wrote:Kieth, Phenidone, by itself, is a very poor, slow speed developing agent, as documented by Grant Haist. The sodium sulfite in that formula is there as a silver solvent first, then an oxygen scavenger, to protect the P. When P or M are combined with HQ they then become what is described as a "superadditive" compound and multiply geometrically the combined effect, hense continous tone development.
Yes Lowell, "in which way do you consider certain types of liquid developers will perform better than those sold in powder form like the old D-76/ID-11 standards and newer formulae like Microphen and Xtol, other than the convenience of them being sold as liquid concentrates?"Lowell Huff wrote:Keith is there a question? What would you like me to clarify?