Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "pr_roark"
<pr_roark@...> wrote:
>
> 
> increasing the pH of the base we use to dilute the carbon inks might
> improve the ink mixes we make.
> 
> Triethanolamine (often referred to as TEA) is, according to Wikipedia,
> often used as a "pH balancer in cosmetic preparations in a variety of
> Paul
> 


Hi,
   Perhaps I can help a bit here.  I am a biochemist, and I've given
more lectures about pH than I care to think about.  What the author at
Wikipedia probably should have written is that TEA is a pH "buffer". 
A buffer is a compound that can readily combine with or dissociate
from hydrogen ions.  By absorbing changes in the hydrogen ion
concentration, the buffer helps keep the pH (which is just a measure
of hydrogen ion concentration) constant when other chemical changes
may perturb it.  Different compounds are effective as buffers at
different pH values.  TEA is a good buffer around pH 8.  

The effectiveness of a buffer also depends on how much is present.  
The usual practice is to make a solution at the buffer concentration
that is needed and then adjust the pH to the desired value by adding
an acid or base.  If you just add TEA to water, it will initially have
a quite high pH, and you would need to add an acid to lower it's pH to 8. 

 What I don't have any idea of is how much TEA would be needed to
maintain the ink solution at pH 8.  Paul's "few drops in 10 mL" would
work out to about 0.1 M, which I would have guessed would be pretty
effective.  I'm a bit surprised that it takes that much to raise the
pH to 8, unless photoFlo is more acidic than I ever realized.

I'm not sure that this helps much, but maybe it provides a bit of
background.

David