--- title: "Pilot Iroshizuku Tsuki-yo: Moonlit Blue Ink Explained" canonical: "https://stationerytimes.com/guides/pilot-iroshizuku-tsuki-yo/" description: "Pilot Iroshizuku Tsuki-yo explained: a dark moonlit blue dye ink in a 50 ml glass bottle, 15–30 s dry time, faint red sheen, low water resistance and origin." category: "Accessories" type: "Fountain pen ink" published: 2026-10-20 updated: 2026-10-20 author: "Ellis Penhale" publisher: "Stationery Times" sources: 8 products: - name: "Pilot Iroshizuku Tsuki-yo fountain pen ink, 50 ml bottle" brand: "Pilot" brand_origin: "Japan" made_in: "Japan" material: "Water-based dye ink in a glass bottle" price_band: "$$$ ($20–75 per item, typical US retail, October 2026)" manufacturer: "Pilot Corporation (Japan); sold in the US by Pilot Corporation of America" model: "INK-50-TY (Tsuki-yo, 50 ml); Pilot USA item 69205" mpn: "INK-50-TY" gtin: "072838692054" url: "https://webcatalog.pilot.co.jp/products/DispDetail.do?volumeName=00004&itemID=t000100002567" --- # Pilot Iroshizuku Tsuki-yo: Moonlit Blue Ink Explained > Pilot Iroshizuku Tsuki-yo is a dark, saturated blue fountain pen ink from Pilot of Japan, named for a moonlit night. It comes in a heavy 50 ml (1.7 fl oz) glass bottle. It's a wet dye ink that dries in 15 to 30 seconds in reviewers' tests, with a faint red sheen and low water resistance. - URL: https://stationerytimes.com/guides/pilot-iroshizuku-tsuki-yo/ - Category: Accessories - Author: Ellis Penhale - Published: 2026-10-20 - Updated: 2026-10-20 ![A 50 ml Pilot Iroshizuku Tsuki-yo bottle drawn in proportion: heavy clear glass, black cap, dark blue ink and a conical recess in the base, beside a dark blue swab card; inset: a nib reaching the last ink around the cone](https://stationerytimes.com/images/raster/pilot-iroshizuku-tsuki-yo-16x9.png) *The 50 ml Tsuki-yo bottle, drawn in proportion, with a swab of the ink.* Original drawing (SVG): https://stationerytimes.com/images/pilot-iroshizuku-tsuki-yo-cover.svg. Drawings © 2026 Stationery Times, reusable with credit under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ## Product facts | Product | Brand | Brand origin | Made in | Material | Released | Price range (typical US retail, October 2026) | |---|---|---|---|---|---|---| | Pilot Iroshizuku Tsuki-yo fountain pen ink, 50 ml bottle | Pilot (by Pilot Corporation (Japan); sold in the US by Pilot Corporation of America) | Japan | Japan | Water-based dye ink in a glass bottle | – | $$$: $20–75 per item | - Made in (Pilot Iroshizuku Tsuki-yo fountain pen ink, 50 ml bottle): Japan. Pilot's Japanese catalog lists the bottle with JAN 4902505367298, which carries Japan's 49 GS1 prefix (it shows where the code was registered), and retailers describe Pilot as making its Iroshizuku inks in Japan (see our Kon-peki guide). We didn't find a country of origin stated on a Pilot page. Source: https://webcatalog.pilot.co.jp/products/DispDetail.do?volumeName=00004&itemID=t000100002567 ## Key takeaways - The standard bottle holds 50 ml (1.7 fl oz); Pilot's Japanese catalog lists it at 271 g. - Dry time is 15 seconds in Goulet's test and 30 seconds in Mountain of Ink's. - A Fountain Pen Companion top-25 list ranks Tsuki-yo 12th of all inks, owned by 518 users. - Pilot's Japanese list price is ¥2,200 (about US$14) per 50 ml bottle, including tax. - Goulet and Mountain of Ink both rate its water resistance low. ## What is Iroshizuku Tsuki-yo? **It's a dark, saturated blue fountain pen ink in Pilot's Iroshizuku line; the name means moonlit night.** Mountain of Ink calls it a dark professional blue, and Goulet calls it one of the best colors in the line. Pilot's Japanese site says Iroshizuku has been on sale since 2007 and that each color is named from a planner's own experience. Tsuki-yo (月夜) was named for the jet-black sea, lit by the moon, seen from an open-air bath on a trip. We couldn't confirm on a Pilot page whether it was one of the line's first colors. It's one of the best-loved Iroshizuku inks. A Fountain Pen Companion top-25 list, shared on Fountain Pen Network in April 2022, ranks it 12th of all inks, owned by 518 users. ## Tsuki-yo specs | Spec | Value | |---|---| | Maker | Pilot Corporation, Japan | | Code | INK-50-TY (50 ml); Pilot USA item 69205 | | Barcodes | JAN 4902505367298 (Japan); UPC 072838692054 (US) | | Bottle | 50 ml (1.7 fl oz), glass; 15 ml mini also sold | | Weight | 271 g (9.6 oz), per Pilot Japan | | Listed size | 82 × 86 × 36 mm, per Pilot Japan | | Ink type | Water-based dye (Pilot Japan) | | Japan list price | ¥2,200 (about US$14) per 50 ml, including tax | | Water resistance | Low (Goulet; Mountain of Ink) | | Dry time | 15 s (Goulet); 30 s (Mountain of Ink) | | Price band | $$$ ($20–75 per bottle) | Pilot's listed size doesn't match the shape of the round bottle, which JetPens lists at 8.0 cm (3.1 in) tall in another color. So our cover draws it in proportion, like our [Kon-peki](https://stationerytimes.com/guides/pilot-iroshizuku-kon-peki/) drawing of the same bottle. ![Tsuki-yo 50 ml and 15 ml bottles to scale, with fills per bottle: about 125 and 37 for a 0.4 ml Pilot CON-40, 62 and 18 for a 0.8 ml LAMY Z28, 28 and 8 for a 1.76 ml TWSBI ECO; water-based dye, low water resistance, 15–30 s dry time, tiny red sheen](https://stationerytimes.com/images/pilot-iroshizuku-tsuki-yo-fills.svg) *How many converter fills each bottle holds (bottle ÷ capacity), with Tsuki-yo's sourced properties.* ## How does Tsuki-yo write? **Wet and dark, with little shading and only a faint red sheen.** Goulet rates its flow high and its saturation high, and says darker inks like this one don't shade much. Mountain of Ink found medium shading and no feathering or bleeding on Rhodia, Tomoe River and Leuchtturm. On Staples 24 lb copy paper it feathered and bled a little. The sheen is subtle. Goulet says a dark red sheen appears with the right paper and nib; Mountain of Ink saw only a small pop of red in large swabs on Tomoe River. ## How fast does it dry, and is it waterproof? **It dries in 15 to 30 seconds depending on the test, and it isn't water resistant.** Goulet measured 15 seconds; Mountain of Ink measured 30 seconds on fountain pen paper. Both rate water resistance low. Goulet adds that the ink is dark enough to survive mild water, but don't count on it for envelopes or signed documents. ## How does it compare with Kon-peki? **Tsuki-yo is the darker, more businesslike blue; Kon-peki is a bright cerulean.** Both are Iroshizuku dye inks in the same 50 ml bottle at the same Japanese list price. | | Tsuki-yo | Kon-peki | |---|---|---| | Color | Dark, saturated blue | Bright deep cerulean | | Dry time | 15–30 s | About 20–25 s (Goulet) | | Sheen | Faint red | Very little | | Water resistance | Low | Low | ## Which pens is it safe for? **Any fountain pen that takes bottled ink.** Goulet rates it easy to clean, like every Pilot ink, though its saturation may need an extra rinse. Pilot's Japanese site says to fit a converter and dip the nib up to the section to fill. A CON-40 in a [Pilot Metropolitan](https://stationerytimes.com/guides/pilot-metropolitan/) holds 0.4 ml, so a 50 ml bottle is about 125 fills; a piston pen like the [TWSBI ECO](https://stationerytimes.com/guides/twsbi-eco/) takes about 28. The heavy bottle has a conical recess in its base so a nib can reach the last of the ink. Goulet also sells Tsuki-yo in cartridges, which fit Pilot pens. ## Where is Iroshizuku Tsuki-yo made? **In Japan, by retailer listings, and its barcode is registered in Japan.** Pilot's Japanese catalog gives the JAN 4902505367298 but no country of manufacture. Pilot lists the 50 ml bottle at ¥2,200 (about US$14) including tax, or ¥2,000 (about US$12.70) before tax. In the US it sits in the $$$ band. Pilot's November 2014 press release launched 15 ml Iroshizuku mini bottles in Japan, sold as sets of three for ¥2,100 (about US$13.30) before tax. One of its three ready-made sets paired Tsuki-yo with Take-sumi and Kon-peki. ## Frequently asked questions ### What color is Iroshizuku Tsuki-yo? A dark, saturated blue. Mountain of Ink calls it a dark professional blue, and Pilot's Japanese site says the name comes from the jet-black sea lit by the moon, seen from an open-air bath on a trip. ### What does Tsuki-yo mean? Moonlit night (月夜). Goulet translates it that way, and US retailers often sell it as Moonlight. ### How big is a bottle of Tsuki-yo? The standard bottle holds 50 ml (1.7 fl oz) and weighs 271 g, per Pilot's Japanese catalog. Pilot added a 15 ml mini in Japan in 2014, sold in sets of three, and Goulet sells Tsuki-yo cartridges. ### Is Tsuki-yo waterproof? No. Goulet and Mountain of Ink both rate its water resistance low, though Goulet says the dark color survives mild water better than lighter inks. ### How long does Tsuki-yo take to dry? 15 seconds in Goulet's smear test and 30 seconds in Mountain of Ink's. The gap comes from different pens, papers and methods, so allow the longer figure on slick paper. ### Does Tsuki-yo sheen? Only a little. Goulet says a subtle dark red sheen can be coaxed out with the right paper and nib; Mountain of Ink saw it only in large swabs on Tomoe River. ### Is Tsuki-yo the same as Kon-peki? No. Both are Iroshizuku blues in the same bottle, but Kon-peki is a bright cerulean and Tsuki-yo a much darker, more saturated blue. ### Where is Iroshizuku ink made? In Japan, by retailer listings, and its barcode is registered in Japan. Pilot's pages we read don't state a country of manufacture. ## Sources - [INK-50-TY｜色彩雫（いろしずく）｜PILOTウェブカタログ (Pilot Japan catalog: Tsuki-yo, JAN 4902505367298, 50 ml, 271 g, water-based dye)](https://webcatalog.pilot.co.jp/products/DispDetail.do?volumeName=00004&itemID=t000100002567) - [日本の美しい情景と季節の移ろいを映す色。万年筆カラーインキ「色彩雫（いろしずく）」。 (Pilot Japan story: on sale since 2007, how Tsuki-yo was named)](https://www.pilot.co.jp/media/story/005.html) - [Goulet Pens: Pilot Iroshizuku Tsuki-yo, 50 ml bottled ink (item 69205, UPC 072838692054)](https://www.gouletpens.com/products/pilot-iroshizuku-tsuki-yo-50ml-bottled-ink) - [Goulet Pens: Pilot Iroshizuku Tsuki-yo, ink review (dry time, water resistance, sheen)](https://gouletpens.com/blogs/fountain-pen-blog/pilot-iroshizuky-tsuki-yo) - [Mountain of Ink: Ink Review #1064, Pilot Iroshizuku Tsuki-yo](https://mountainofink.com/blog/pilot-iroshizuku-tsuki-yo) - [Fountain Pen Network: List of inks by popularity (Fountain Pen Companion top 25, April 26, 2022)](https://fountainpennetwork.com/forum/topic/366055-list-of-inks-by-popularity) - [万年筆用インキ『色彩雫mini』新発売 (Pilot Japan press release, November 20, 2014: 15 ml mini, sets of three, Tsuki-yo × Take-sumi × Kon-peki set)](https://www.pilot.co.jp/press_release/2014/11/20/iroshizuku_mini_3.html) - [Serai: パイロット『色彩雫』 sold since 2007, 24 colors](https://serai.jp/kajin/1114437)