Diamine Regency Blue is a 150th Anniversary series blue ink that is sold in a special triangular glass bottle.
Regency Blue is a wet flowing blue ink that is well behaved and a reasonable choice for day-to-day use. It’s sold in a slightly smaller-than-normal 40 ml glass bottle.
This in has some shading but the darkness means that the shading and the red tones inside the chromatography results are almost entirely lost on the page. It remains a handsome blue ink, but lacks some of the subtly and sophistication of the competition.
In practice this is a very nice blue ink that writes like a blue black ink and stands up well to daily use. It’s relatively quick drying and the lack of shading means it works well for office use, where fancier characteristics may not be desirable. The ink can appear to be purple-ish in some lights (because of the red tones) which may not be something everyone enjoys.
Regency Blue has very low water resistance. Some sheen can be seen depending the paper used, but it’s generally quite tame.
Diamine Regency Blue 150th Anniversary Fountain Pen Ink Information