It's not really mentioned here very often, but Platinum blue-black, at least according to Platinum is an iron-gall ink. You can look here.
Platinum blue-black is one of my favorite blue inks. My mom used to use it a lot when she was younger. It's also one of the only iron-gall inks available in cartridges. MB doesn't even have iron-gall inks in cartridges. That said, I have a lot of odd information about the ink since we have loads of it everywhere in my house, even in places where we wouldn't think to look. It was also the ink I chose when I bought my Nakaya. They were really nice and gave me a complimentary bottle.
Let's start on time based stuff.
The ink starts out on paper quite blue. The ink slowly changes color on paper to a greyer, more steel blue color. Three days is enough to change it noticeably to the more "mature color." It's hard to see, but the top line is older, and the entire second line is fresh, and bluer.
If you are curious about the waterproofness of the ink, the longer the ink stays on paper, the more permanent it gets. If you put freshly written stuff under the sink, it will run slightly, but after three or so days, there isn't any running at all. The ink stays put. It's really waterproof. No matter what I did to it, it didn't go anywhere. After the paper dries, the ink turns greyer still, but there is still no running or bleeding.
About longevity in the cartridges, after many years, the ink as does all other inks, dries up in the cartridge. I don't know what plastic Platinum uses, but the cartridges end up half-full after nearly twenty years. This is better than most cartridges. I have some 1/3 full Pelikan cartridges from about five years ago. The ink though, turns grey and gets tiny chunks in it that taste like iron. (Nasty, I know. Thanks mom, for having an old stash of these cartridges somewhere in the house)! I was 10, and was cleaning a pen that we put one of the cartridges into. If cleaning a pen that used this ink, if the ink was allowed to dry inside, one would need to take out the feed. The little bits and pieces will wash away quite easily.
Corrosion. Well, many Platinum pens that have used this ink that have the plated gold nibs get the nibs eaten away or corroded or in some cases, the plating flakes off the nib. Platinum talks about this in link above. My mom's pen (burgundy from the early 70's), and my pen (purple from the 1960's) both had gold nibs, and we didn't have this problem, fortunately, but I've seen loads of 70's Platinums pens with gold plated steel nibs that corroded. Platinum pens are crazy common in my family, and you can find them in strange places too. It doesn't seem to attack the rubber seals or the plastics used in the pens though. Our pens both have intact seals. Oddly enough, it doesn't seem to attack the plain steel nibs or the stainless steel ball in the cartridge much at all. One of my sisters has a Platinum pen with a plain steel nib from the 70's, and the nib is completely intact even though Platinum blue black was used in the pen.
How about the ink eradicator? Depending on the age of the ink, as in how long it was on the paper, the ink eradicator, as with Montblanc Blue-Black, another ferro-gallic ink, will remove the blue parts, leaving grey on the paper. The longer the ink stays on the paper, the less it will be able to eradicate.
How about reaction with the paper? My mom's notes from 40 years ago seem quite intact. It looks like the color stabilizes after a few months as a nice steel blue. I've heard that most modern ferro-gallic inks don't really eat paper like their older counterparts because of newer chemicals and ingredient being available.
As far as I can see, the ink doesn't stain. I have some vintage Platinum cartridges of blue-black from the 60's and 70's that I cleaned out, and they cleaned out completely. My newer cartridges are the same way.
Here is a photo of fairly fresh Platinum Blue-Black where one word was soaked in water. The scanner I use has a CIS sensor, so stuff that doesn't touch the glass isn't as clear, and the part of the paper that was soaked was wrinkly after I dried it. "Steel" is after water and "blue" is untouched by water. I ran the paper under the sink for five minutes. As you can see, nothing ran at all, but the ink turned greyer. So, if you and your notes in Platinum blue-black go under water, you don't need to worry too much.
Edited by Dillo, 07 October 2013 - 00:22.