Old Dogs and New Tricks.
Eco Flo Professional Waterstain
OK, so I hate change.  I'm big enough to admit it.  But I don't have to like it (like wearin' readin' glasses to see my work).  However, there are a few occasions when change isn't that bad.  I'm plannin' some "modern" types of holsters and gear, so I wasn't opposed to tryin' a "modern" finish on 'em.  I have resisted trying the Eco Flo Professional Waterstain that has been around for a while. But, the opportunity has presented itself, and I tried it.  You know, it's pretty spectacular stuff!
I needed to make a paddle holster for a friend and decided to try Eco Flo for the finish.  I had heard there wasn't a problem with it rubbing off on clothes, even when they got wet. Well, that would be the type of finish I would need on a paddle holster.  So, I gathered up the Waterstain, the Clear Matte Finish, the Edge Dressing, the Conditioning Creme and the high density foam blocks that can be used with the finishes.  
The directions said to shake bottle vigorously, and apply the Waterstain directly to the foam block.  While it is out of character for me to follow directions, I did it just this once, to see how it works.  Then the directions said to apply it to the leather in a circular motion.  So, I did that too.
It went on real easy.  I did actually use different types of strokes to get the Waterstain moved around the leather, but I always finished off with the circular motion.

You could tell when it was too light, and just applied more to that area.  But, when there was plenty on there, it became a consistent color and didn't change after that.  It was pretty easy. 
Since I'm Scotch, I decided to rinse out the foam right away for the best chance of saving it for another application.  I needn't have worried.  While the pigment stayed in the foam block, it rinsed clean enough that it wasn't stiff.  However, I didn't like all that pigment being wasted in the block.  I decided to see how my smaller high density foam brushes worked next time.
I put the leather in front of a fan and let it dry for about an hour.  Then, I used one of my foam brushes and dampened the flesh side of the leather so I could burnish it down.

The water reluctantly dampened the treated leather, and it burnished down real well.  The edges burnished well with a little water also.  I'd have to say, it burnished better than with oil dye.
The directions called for buffing the Waterstained surface.  I pulled out an old T-shirt and buffed away.  It looked pretty good.  At that point, it was time for the Matte Finish.  I decided to put that on with one of my foam brushes rather than one of the big foam blocks.
The Clear Matte Finish was shaken and went on very creamy.  I worked it around in the circular motion.  I may have put it on before the Waterstain had time to completely set.  I had just a faint bit of Waterstain come up with the application of the finish.

It went back in front of the fan, and in about fifteen minutes I figured it was dry enough I could start sewing.  The holster went together quickly.
When the holster was sewn up, it was time to put this "new" finish to the test. Since it had been less than two hours since I had started using the Waterstain, I figured it might not have had time to set.  I was prepared for some bleed when I dampened the holster to wet-fit it to the revolver.  I completely submerged the holster, and allowed the moisture to work its way into the leather's fibers.

On the back, where it wouldn't be evident, I took an old T-shirt and scrubbed on the finish.  The look of the damp finish didn't change, and ABSOLUTELY no color came off on the T-shirt.  I have to tell you I was amazed!
Next came the edge dressing.  Again, I used a foam brush so I could have more control.  The edge dressing went on smooth and thick.  It dried quickly.

It looks like a very durable finish. Time will be the ultimate test, but for ease of application, it doesn't get any better.
Then came a light coat of the conditioning cream. This also dried quickly.  It seemed to give the finish a deeper, softer luster.

The directions didn't say to buff it out, but I have a hard time following directions, so, when it was dry, I buffed it out anyway. 
That gave it a nice warm glow.
I'm pretty sure I didn't do everything the way it was supposed to be done.  My buddy Byron (who manages the Des Moines Tandy Leather Factory outlet) told me to let it dry overnight between each step.  I said I would, but we both knew I would be too impatient.  It's a bit of a joke between us that it takes me too long before I realize his advice should be followed.  But, eventually, I always come around.  This time, however, there doesn't seem to be any downside to my impatience (yet).  
I'm happy with the way it turned out.  I have to say, I really like this finish for modern gear.  It is easy to use.  It seems to be much quicker than conventional oil dyes.  It doesn't come off when wet, even when rubbed vigorously.
Allright ... after some conversations with folks who have used Waterstain, I decided I had to do a stain penetration and abrasion test.

One of my thoughts was that better stain penetration might be achieved by dampening the leather.  So, here on a scrap of a project, I have dampened one side of the line.  You can see the water has saturated the epidermis layer and is into the fibers below.
Here, I have applied an equally heavy coating of black Waterstain to both sides of the line.  You could already see the penetration was darker on the dampened side to the right.  You can even see it in the photo if you look hard enough.
This is how the coloration looked after it had dried.  You can see a deeper, richer hue of black on the right where the leather was dampened.  The dried Waterstain looks a little bluer on the dry side.  It was more noticeable in real life than in the photo.
Without adding a finish or conditioner to protect the Waterstain (which is not recommended for actual projects) I folded the leather and drug it across 60 grit wet/dry sandpaper (which also is not recommended for actual projects!).  The top mark was made with moderate pressure.  The middle line was made with lighter pressure.  The bottom markings were made with the leather not folded so the pressure was not concentrated in such a small area.

In this close-up, the richness of the coloration can be seen between the dry application on the left, and the dampened leather on the right.  You can also see a definite difference in the increased penetration of the Waterstain on the damp side of the test.  While both sides lost coloration with abrasion, the coloration on the damp side to the right was deeper, and resisted abrasion better, than the dry application on the left.

With hindsight, I'm wunderin' if I couldn't have gotten deeper coloration penetration if the leather had be dampened all the way through.  However, this test was sufficient to convince me to apply Waterstain while my leather is damp, rather than wait for it to dry (which could speed up the production process).  
The color penetration is deeper, and with the Waterstain Finish, and Waterstain Conditioner, I'm certain the product would handle the abrasion test better.

I guess that means I'll have to do some more tests...
So, this time I worked with leather dampened completely through, as seen in the photo above left.  A heavy, even coating of black Waterstain went down on both the dry and damp portions of the leather.  Even when still damp, you can see in the photo above right, the Waterstain goes on richer and deeper on the damp leather.
I allowed the leather to dry overnight.  In the photo above left, you can see the coloration between the dry and damp sides of the test leather is even more pronounced when dry.  Then, one thin coat of Finish (clear matte) is applied over the Waterstain black.  When dry, this was buffed out with an old T-shirt.
After buffing, I applied a coat of Conditioning Cream, as seen in the photo above left.  When it was dry I buffed it out and applied another coat of Conditioning Cream and buffed that out, seen in the photo above right.  The deeper coloration of the Waterstain applied on damp leather is noticeably richer and deeper.
Now for the abrasion test!  The abrasive mark at the top was made by folding the leather over and running the folded edge of the leather on 60 grit wet/dry sandpaper.  The first pass with moderate pressure didn't leave much of an abrasion, so I did it again two more times, with increasing pressure, till I got the mark shown above.  The added coating of finish, and two coats of Conditioning Cream, armored-up the finish nicely!  Upon close inspection, you can see more of the coloration did come off on the dry application side of the test.

The middle abrasive mark was made by once again folding the leather over, and running the folded edge across 60 grit wet/dry sandpaper.  This time I only used moderate pressure and one pass.  As you can see, very little coloration was lost on either side.  However, I do believe I detect a little more color loss on the dry applied side on the left.

The lower, and third abrasion test, was made by laying the leather flat on the 60 grit wet/dry sandpaper and rubbing it around.  Again, I detect a little more color loss on the dry applied side.

In Conclusion:

After the tests I have conducted, I would say Waterstain coloration penetrates deeper when applied to leather that is damp all the way through.  The color is most definitely richer.  With two coats of Waterstain finish and two coats of Conditioning Cream, the finish is amazingly resistant to abrasion.  When the abrasion is aggressive enough to remove the top layer of leather, the damp applied Waterstain coloration penetrates deeper than it does when dry applied.

I have to say I am favorable impressed with the Waterstain line of products, specifically for its colorfastness when wet, and will be using it on my modern production gear from now on.  Just goes to prove, old dogs can learn new tricks.