Identity & Provenance
i.
The maker, the year, the line — and the language of the name itself.
BrandPilot · Iroshizuku
ModelTsuki-yo · 月夜
EnglishMoonlit Night
LineIroshizuku · "colour droplets"
CountryJapan
Year introduced2007
Archive number№ 014 / 64
StatusIn production · widely stocked
Colour & Hue
ii.
The primary read, the pool at the trough, the sheen at the angle, and how much the colour shifts as it dries.
Primary hex#1C2C47
Primary oklchoklch(24% 0.06 252)
Colour nameMoonlit Night
Hue familyBlue-black
WarmthCool
Shading (high)#3A4B6A — surface mid-tone
Shading (low)#0E1828 — deep pool
Sheen colour#B87333 — copper
Sheen angle~ 30° from page
ShimmerNone
Wet vs dry shift22 / 100 — modest
Chemistry
iii.
The liquid itself — pH, viscosity, how it behaves in the bottle and inside a demonstrator.
pH7.4 — slightly alkaline
Viscosity (cP, 20 °C)2.2 cP
Surface tension42 mN / m
Dye loading~ 3.4 %
Water resistanceNone — not permanent
PermanentNo
ArchivalNo — ISO 11798 not claimed
Bleach resistantNo
MaintenanceLow
Demonstrator safeYes — no staining observed
Behaviour on the Page
iv.
Wetness, saturation, sheen, shading — and how feathering and ghosting test on standard cream.
Sheen visibility5 / 5
MatteVisiblePronouncedMirror
Behaviour on creamRicher · sheens more
Behaviour on brightCrisper · sheen muted
Dry Time · by Nib
v.
Seconds to a smudge-free pass on the standard cream paper.
Left-hand viableWith patience · EF preferred
Test paperTomoe River S · 52 gsm
Pairing & Best Use
vi.
Where this ink belongs in the cabinet — by nib, by paper, by occasion.
Best for nib size
M
B
BB
Stub
Soft
Best for paper tone
Cream
Ivory
Bright white
Best for paper finish
Smooth · sized
Vellum
Best for use
Correspondence
Journaling
Margin notes
Signatures
Best for hour
Evening
Night
Afternoon
Avoid for
Document-archive
Waterlogged hands
Coated paper
Recommended pens
- Pilot Custom 823№ 003
- Sailor Pro Gear№ 038
- Pelikan M800№ 011
Recommended papers
- Tomoe River S№ 001
- Apica CD Premium№ 071
- Sailor Profit Note№ 089
Editor's note · M. Hoshino
An ink the rest of the cupboard is benchmarked against. Lay it down with a generous nib on a paper that refuses to bleed, and the night arrives on the page in the time it takes to turn off the desk lamp.
Colour story
From the line of Iroshizuku — "colour droplets" — each ink named for a moment in the Japanese natural year. Tsuki-yo is the moon, viewed from a window, on a night cool enough to want the lamp on.
Bottle
50 ml · Iroshizuku flask
Glass · cork-stopper
Tier II · $ 0.56 per ml