Digital BW, The Print

"horstenj" <j.h.j.h@...> wrote:

> ... To pre-empt subsequent questions as it turns out that we in Europe have difficulties to get exactly the same chemicals as you have used:
> 
> 1) Tergitol: what is its purpose?

It's one of the surfactants.  This is is from Dow and appears to be highly thought of.  It incrementally improved, particularly, the Arches performance when added to the C6b mix (Photo Flo and LFN).  The removal of either one of the previous surfactants decreased smoothness.

My observation is that one of the variables that is very important is the nature and mix of surfactants or wetting agents that are used.  They affect droplet formation, paper penetration, bleed, cleaning -- a fair number of performance parameters.  In general, we want non-inonic surfactants that are compatible with the other ingredients.  It takes a mix of different types.  They'll line up on the water-X surface differently depending on what that X surface is -- air, paper, metal.  They tend to be types of alcohols (as is glycol) that are water soluble.

Photo Flo has Kodak's proprietary version of this type of alcohol in it.  

Edwal LFN has 3 different alcohols in it.

> If we can't get the exact same version, what is essential to pay attention to?

Go to http://www.dow.com/surfactants/products/second.htm and click on the Tergitol 15-S-7 link, as well as a few others.  A number of the specs on that sheet are important, and I cannot recall all the specifics.  (I read, learn, try the most likely few, find a solution that works and move on, largely erasing the blackboard.)  At one point I understood the cloud point, HLB, pour point, CMC and some of the other variables and found the 15-S-7 to be one of or the most appropriate in the Dow group.

I have very crudely found that about 1% of these gives most of what you can expect of them.

There may be better, but at some point one has to make a decision and move on.  There is no doubt room for improvement, but when the high res scans show me that my mix is matching the OEMs and otherwise working well and consistent with what I'd expected, it's time to work on some other variable (not necessarily ink or even printing related).


> 2) Edwal LFN: again, what is its purpose? Looks like a similar chemical as Photo-Flo.

Yes, it was mostly chosen as a good surfactant that had a good history in the photo field.  I think it's similar to the Tergitol.

> What's the difference (Can't we increase the level of Photo Flo 600? I'm just speculating that you couldn't because of the glycol level...).

Photo Flo 600 has 3 times the surfactant per volume of the 200.  So, you might think that decreasing the amount would work.  That is where I suspect you might run into a mix that ended up with too little glycol.  However, there is probably some percentage of PF 600 that gets you all the surfactant action you need and still has enough glycol.  I'm guessing it's less than the 10% is use for PF 200, but I just have not done those experiments.  If 5% works and does not make for a cloudy solution, then you might just go with it.

You might be able to increase the amount of PF 600, but even aside from whether the amount of glycol would peak and start detracting from smoothness, I found more of the Kodak surfactant over the amount in 10% Photo Flo did not make smoother prints.  It takes different types of the molecules, not just more of the same type.  In addition to different surfaces needing different surfactants, even those that line up on the same surface may have different characteristics that are complementary.

> If we need a replacement, what could be an alternative?

I didn't try the Ilford because I did conclude some glycol helps and it had none. Ilford's might be worth a try, in addition to the PF 600.

You can start simple and just test different mixes.  I used 1600 dpi scans of prints -- simple test strips that had identical patches -- and then just compared them to each other.  If you have some Epson K3 LK and LLK to use as standards for comparison, you'll see how you're mix is doing.  

Hope this helps.

Paul
www.PaulRoark.com