Then, I saw this other invisible ink in 18ml bottles on eBay, with no brand name or detail -- including whether it's safe for fountain pen use, much less whether it's "bulletproof" -- for just a few dollars and came with a tiny UV torch, I bought one just for the hell of it, even though the per-millilitre unit price is 220% of that of the Noodler's ink.
However, since then I was able to order a bottle of Blue Ghost sold and delivered by Amazon US for a reasonable price, so I had confidence it was actually in stock. That order was delivered yesterday. (I have since cancelled my original order from the first retailer and got it refunded.)
I wonder how many of us here would bother with getting two different invisible inks, even though we wouldn't blink an eye about ordering the sixteenth "different" shade of blue, or even coloured two inks that are supposed to dopplegangers of each other?
Anyway, so here they are:
Both are equally invisible on the page under normal lighting conditions, of course.
Once dried, you can write on top of it with coloured inks, with minimal interference (feathering, etc.) and certainly not every place where two ink tracks cross, but there is nevertheless some with either of the invisible inks if you look closely.
Neither of the inks are what I'd call waterproof (but they are fairly water resistant), which I guess precludes them from being "bulletproof". This is what they look like after a two-hour soak:
Even though the Wing Sung 3008 into which I filled the Turritopsis ink has an EF nib, and the Sailor Profit Junior that holds the Blue Ghost ink has a MF nib, I don't expect the difference in the line widths to be substantial. What I'm finding, though, is that Blue Ghost has more of a tendency to spread once laid on the page. The paper in the Maruman m.memo DMP-A7 notepad I used there is not apt to be absorbent, and I was careful to cover the rest of the page with a paper napkin while I wrote, so as not to compromise the paper coating. (I can see from the washed out writing how fine or broad the contact surface from the nibs are. (Yes, I can test them properly against each other with a different ink, or even swapping the inks around in the pens, but right now I don't feel like cleaning them and flushing ink down the drain.)
Between the lack of evidence to support the claim of being "bulletproof" (but I really should look up if there is any word definition and test procedure published by Noodler's), and the tendency for the lines to be broader than they need to be because of the spreading, I must say that the Blue Ghost ink has disappointed me, if so no-name ink (actually, there is one in 3-point Flyspeck on one side of the bottle label: Tramol) from China proves equally as water-resistant but seems to work better. Now, of course I don't actually trust or assume the Turritopsis ink to be perfectly fountain pen safe, so I'm not going to put it in a $200+ gold-nibbed pen, but then I'm not inclined to do so with Blue Ghost (or Noodler's inks in general) either; a Sailor Profit Junior which cost me twenty-odd bucks to acquire is about as much as I care to risk on a lark.
Still, writing with invisible ink is fun, and more fun (and much easier!) when my order of UV bulbs for my desk lamp comes in. I can't wait to show the young'uns at the next Christmas family gathering, and I've already put in an order for some non-fountain pens that also dispense invisible, fluorescent-under-UV-light ink to give them -- and a couple of big UV torches for their parents; I'm sure they'll need those.
Edited by A Smug Dill, 12 July 2019 - 22:03.