A Note About My Ink Reviews:
All of the images in my reviews are scanned at 1200dpi on a Brother MFC-J6720DW in TIFF format, converted to A4 at 300DPI in Photoshop CC, and saved as a compressed JPEG. All scans were edited on a color calibrated ASUS PA248Q with aΔE<3 to ensure maximum color accuracy.
TL;DR: The colors should be as accurate as is possible.
Not having a suitable green (well, any green at all) in my ink collection, and not having any Montblanc ink to speak of, I decided to pull the trigger on a full bottle of Irish Green from Amazon. Rarely do I ever feel like buying a full bottle sight unseen (aside from such reviews as I can find on the internet), but in this case I liked the color enough and the price wasn't awful, so I bought it, along with Lavender Purple (also Montblanc) at the same time. I usually prefer blues to anything else, with my go-to being Diamine ASA blue, with the backup of Noodler's Midway Blue for the times I need something more water resistant. I have a single black, Noodler's X-Feather, and then Noodler's Apache Sunset, J.Herbin Stormy Grey, and Diamine Oxblood, and those have been my only inks for ~18 months, and I felt like I needed something new and more exciting.
Enter Irish Green.
So let me delve into the properties of this ink for a moment. Scores, where applicable, are represented on a 10-point scale, with 10 being better/larger than 1.
Flow: When I tested this in my Edison 1.1 Stub, which is quite the wet pen, I found the flow to be wet, as expected, but not so wet that I found it difficult to use on lesser papers. What I did find, however, on lesser paper, is that the ink loses some of this flow and becomes a bit dryer when writing, and this is a noticeable difference, but should not be troublesome to most potential users.
Saturation: This ink is what I'd describe as a very saturated shader, but this could be due to the properties of the test pen. Stubs (at the very least the ones which I have had the pleasure of using) seem to have both a darker, more saturated output, but also seem to encourage shading.
Lubrication: Better than most of the ink I own, but I have tried a sample of the Noodler's eel series and can say that it is similar. Very smooth, very much like glass, but not uncontrollable like some I've tried in a stub.
Show-through: Virtually none on any of the Clairefontaine paper's I've tried, but quite a lot (as expected in a wet stub) on cheaper paper. Rhodia 90gsm as well as 80gsm Rhodia and CF Triomphe etc. handle it very well. Copy paper (which is what I did the review on) shows significant show-through, and the back of cheaper papers is simply not usable.
Shading: It varies with the nibs used (also tried this ink in a Visconti Rembrandt M, and got almost no shading), but is usually enough to be noticed, but not enough to qualify it as one of those inks that is nothing but shading. Also varies with the paper used, CF and Rhodia papers which are less absorbent exhibit more shading.
Bleed-through: None, even on cheap papers.
Spread: None noticed on any of the tested papers. (Rhodia, CF, and #22 copy paper)
Smear (dry): None on any of the tested papers. (Rhodia, CF, and #22 copy paper)
Feathering: Extremely slight (not noticeable unless you look for it) on less-than-FP friendly paper, but none on higher quality papers.
Water resistance: While it wasn't sold to me as water proof or resistant, and I fully expected it to wash off the page, I could not get it to rinse off. *Dry time for the water test was roughly 12 hours after it was applied to the paper, if immediate water resistance is your primary concern. (In which case I recommend X-Feather, from personal experience.)
Other: The color is nice, but not so vibrant to be in your face and scream at you, but rather it is more of a muted plant green. It reminds me of foliage, to be honest, which isn't a bad thing, but it isn't light like Gruene Cactus Eel or dark like Diamine Sherwood green. It has quickly become one of my favorite inks for annotations and some general notes, but I don't think it fits for general writing, simply due to the fact that it is green. I have experienced no startup issues or nib creep. On another note, I really like the bottles, as they are both a significant design departure from Noodler's, Diamine, and J.Herbin bottles that I've owned.
Overall, I am highly impressed by my first Montblanc ink, Irish Green.