Read the review for curiosity or nostalgia sake but I'm not sure where you'd find this ink if you wanted it.
I reviewed the sample in my Pilot Vanishing Point with broad nib.
Bottle and pricingBottle capacity: unknown
Price / ml: unknown
Color and saturationPrivate Reserve Invincible Black is, well, black. A very dark black in fact. Side by side with Noodler's Heart of Darkness it looks even darker.
I also compared it with Noodler's Whaleman's Sepia, just for reference, even though the latter isn't technically black.
ShadingPrivate Reserve Invincible Black is black as the night and thus pretty much flat.
BleedthroughPR Invincible Black bleeds less than I would have expected, even on cheap paper. There's evidently some ghosting but even that comes more from the contrast between the very dark ink and thin white paper than from actual penetration.
Flow, lubrication, and smoothnessInvincible Black flows nicely and smoothly in the Pilot Vanishing Point with the broad nib unit. However, I have noticed that it likes to dry up rather quickly in the pen, within a few hours. This makes for hard starts and it's definitely not a feature I appreciate, especially in my most expensive pen.
Drying timeHere's the rub. Umm, pun not intended, but you'll see... Private Reserve Invincible Black dries reasonably fast on cheap paper and even the shinier and more expensive stuff like the Clairefontaine 90g sample. Keep reading...
Smearing when dryFollowing up on the previous section, this ink is quite prone to smudging when rubbed. So even though it is technically dry, it needs a lot more time to become inert, and even then you can still get it to smear a little if you rub it hard.
Water resistanceAs advertised, Private Reserve Invincible Black is completely water resistant and immune to the elements (not sure about acid rain though).
ConclusionThis review might have been all for nothing, considering Private Reserve Invincible Black has been discontinued, but it was interesting, nonetheless, to see how it behaves in relation to other waterproof inks. Overall it's a decently performing ink, with two exceptions: the drying up inside the pen and the fact that it likes to stain containers, including the Pilot VP's converter. Since it's extinct, if you are looking for a black water resistant ink my only option is to recommend one of many such variations that Noodler's makes, including Heart of Darkness and another black ink that I will review soon.
Following are the two samples on photocopy and Clairefontaine 90g paper, respectively.