Basic Glycol/TEA Related Questions

[craigclu]

I've found tidbits relating to this but wanted to know directly your thoughts on:

What blend of propylene glycol to TEA is enough to thin the viscosity at lower household temperatures (ie, 60 F°)?

What is the general solvent effect difference as one blends in the PG vs straight TEA?

My understanding of Dimezone-S vs Phenidone is that the Dimezone is more stable in water solutions. Is there any advantage for using it in PG/TEA type of concentrates?

Will the PG interact any differently with concentrate solutions (vs straight TEA) when Pyrogallol is involved?

I'd better quit adding items to this post for now!

 

[john_s]

I was told by one potential supplier that TEA "99%" is solid at cool room temperature. Another from whom I purchased some TEA 99% just today has supplied a liquid which is far from looking like solidifying. They told me that it depends on what the other 1% is: in this case, it's (mostly) diethanolamine and ethanolamine. I hope that these compounds do not have any unwanted effects. It's certainly convenient to have it in liquid form. (It came, incidentally, from a company that blends highly specialized lubricants for industry)

 

[Tom Hoskinson]

I was told by one potential supplier that TEA "99%" is solid at cool room temperature. Another from whom I purchased some TEA 99% just today has supplied a liquid which is far from looking like solidifying. They told me that it depends on what the other 1% is: in this case, it's (mostly) diethanolamine and ethanolamine. I hope that these compounds do not have any unwanted effects. It's certainly convenient to have it in liquid form. (It came, incidentally, from a company that blends highly specialized lubricants for industry)

The small amount of diethanolamine and ethanolamine do not cause any problems in my experience.

As the TEA gets colder, its vicosity increases - get it cold enough and it will freeze. My current supply starts to solidify around 60 degrees F.

To reduce TEA viscosity you can dilute it up to 50/50 with Propylene Glycol. In my experience, the only downside to this is that with highly diluted working developers you may need to add some alkali.

 

[gainer]

TEA can be supercooled below its normal freezing point. Diethanolamine and monoethanolamine will increas pH. The Dow website shows different curves for two different grades of TEA.

I have had success by dissolving the ingredients in propylene glycol and adding an equal amount of TEA to make a single solution stock. You simply double the amount. If you would normally use 1+50, use 1+25. It is less flexible this way, but you can always add more alkali to the working solution if you want more activity.

 

[Gene Johnson]

Pat,

What about mixing the TEA and Glycol first, then mixing in the Phenidone and Vit C? That way we could maintain the high concentration that is so handy?

 

[Gene Johnson]

True,

I have no firsthand knowledge of this but have heard that the pH of the straight TEA 1:50 is a bit on the high side.

So now I guess I should ask if this is so. What is the expected pH of PC-TEA prepared 1:50, and is it really high-ish? And, what would the expected change in pH be after diluting the TEA 50/50 (for example) with , say, glycol? And would that be better or worse, all things being equal?

 

[Tom Hoskinson]

Sounds like an opportunity for some experimentation and measurement.

 

[john_s]

Isn't the advantage of TEA supposed to be its buffering? So shouldn't further dilution have a minimal effect on the resulting pH?

 

[gainer]

Isn't the advantage of TEA supposed to be its buffering? So shouldn't further dilution have a minimal effect on the resulting pH?

The idea of TEA as buffer was not my idea. I see by the Dow information about MEA, DEA and TEA that pH varies with concentration. The less pure grades of TEA have somewhat higher pH because they contain MEA and/or DEA.

Sometimes it is best not to be too concerned with theory. What you think you know can spoil your fun by keeping you from trying something unorthodox.

TEA's change of color can occur on heating. The amount of water that a batch can absorb is limited to the amount contained in the air in the neck of the bottle. You have the same trouble with HC110, which contains ethanolamines, yet it is known for long life of the stock solution.

I think the best bet is to dissolve the developing agents in glycol and dilute that solution with an equal amount of TEA to make a single solution stock, or to add TEA as the B solution of a 2 part stock system. The latter is more versatile, the former is more convenient.

 

[gainer]

A little more info.

First, look in www.dow.com for all you ever wanted to know about MEA, DEA and TEA.

In a nutshell, the pH of a TEA solution is about 10 for a 1% solution of commercial grade and about 9.75 for 99% TEA. The pH changes about 0.2 when the concentration is doubled or halved all the way up or down a logarithmic scale. So, a 2% solution of commercial grade TEA would have a pH of about 10.2 and a 1/2% solution would be about 9.8. I suppose that constitutes buffering. The actual pH will depend on how much of it is used in neutralizing the ascorbic acid.

The diluted working solution, if the solvent is all TEA, will surely have between 1/2 and 2% TEA, so I would expect the pH to be between 9.8 and 10.2 if you use commercial grade. I don't see any point in spending the extra money to get 99% TEA as long as the commercial grade is consistent, and I suppose it to be or Dow would not be so specific about its numbers. Is there a proportionality between developing time or contrast and pH? I don't know. Rather than theorize, it's more certain to experiment IMHO.

 

[Gene Johnson]

I like to experiment too. From the chart on the Dow website, the pH of a 2% TEA solution looks to be about 9.9, a 1% solution about 9.7, and a .5% solution about 9.5 or 6. Not such a big difference? I can't remember who it was on the pure-silver list that reported excellent results from the 50/50 mixture, but it was somebody I trusted. So what I'm getting at here is that we could make up the concentrate from a 50/50 mixture and end up with a working solution pH between 9.5 and 9.7 for developer dilutions between 1:50 to 1:100.

Theoretically. When my current batch is gone, I'll give it a try.

 

[gainer]

I'm sure it will work. Just don't be too upset if the very high dilutions are being starved. At 1+50, you get only 2 grams of ascorbic acid in a liter of working solution. That seems to be about as active as D-76 when the solvent is all TEA. Now, if you are going to mix half and half glycol and TEA for solvent, relatively more of the TEA goes to neutralizing the ascorbic acid. In other words, the net pH of the whole mess and the availability of enough reducing agent to do the job before it peters out are both concerns. But you're going to experiment, so have at it.