Well, I finally put my parking solution together, and tried it out on a blade! I took some pics, here they are with commentary.
My setup consists of a tank made from 3" x 6" x 20" rectangle tube, mild steel. I know stainless is more commonly used, but Eduardo showed that he uses mild when he shared a WIP including that, not long ago. Found out that once the inside of the tube is parked, it's pretty impervious to further corrosion from the solution. Plus, I had the tank already from something else.
I bought a fry thermometer to keep with the tank, and set it up on my good Wells hot plate.
I got the parkerizing solution sold by Midway, made by Lauer. A gallon will make five gallons of solution, mixed to full strength with water.
My tank will hold about 1-1/4 gallons, so that's perfect to make a 1 gallon water, 1/4 gallon phosphate mix.
I heated the mix to 180f, the recommended temp from Lauer, degreased some steel wool, and immersed that in the tank for about 45 minutes.
It bubbled a good amount, tapering off toward the end. The solution was easy enough to keep within 10 degrees, adjusting the plate as necessary.
I finished etching, scrubbed off the oxides with clean bottled water and an old toothbrush, and put the wet blade right into the park tank.
It fizzed nicely, and I kept it there for about 45 min. The fizzing had quit when I pulled it out.
First off, it was jet black all over. It dried itself form the heat, although a section of the edge had a water drop that dried slower and left a white mark.
I heated it a bit over the plate and rubbed coconut oil into it. The coating drank it up.
After warming the blade a bit further, then letting it cool, I started in sanding it. Normally I use 1500 grit paper for this, but I was out of 1500 so I tried 2000.
The coating ate it alive- it's a kind of abrasive surface. I switched to 1200 grit paper. Even then the paper burnt right up, but it had more of an effect, removing the black coating. This stuff is tough! It holds up to sanding quite well.
It took a little work to get down through the black coating, and start shining up the 15n20 layers. Here's how it looked when mostly brought out:
Some disjointed ramblings on the matter:
I should have etched deeper. I just topped up my etch tank, and need to adjust it to be stronger yet. Nevertheless, the results were quite good. They could be better though.
It seems to get quite black, although I did not use the "pre-black" solution they sell. Perhaps, as I read elsewhere, the fact it had just been ferric chloride etched does pretty much the same thing.
The shiny areas, after sanding, did display some light hazing of micro-pitting. This was from the park. I may in the future lightly sand after final etch and scrub, so that the high layers do not benefit from the pre-etch of the ferric, and thus hopefully are not as susceptible to the action of the park.
I may run a little more dilute. I have seen references to as light as 1:10 for damascus, although that may have been a different brand solution. Nevertheless, the results I got were pretty much what I hoped for right off the bat.
In the low areas, the black was quite resistant to being sanded off, just like I want. A deeper etch yet would only improve this. When oiling after final sanding, hardly any black showed on the oily towel, all that dark staying on the blade like I want. Sahweet!
I'll be refining my process a little more, several fancy integral chefs to finish the next week, so I'll post what else I find.
By the way, here's a final look at how that santoku came out.