(Thank you Steve for a generous sample of this lovely ink!)
Sailor, the Japanese manufacturer of pens and inks, recently discontinued their previous line of Jentle ink and replaced them with some new Jentle colors. Sailor Souten, or Azure Sky, is very similar to the discontinued Sky High ink in terms of color and red sheen. Souten is actually also quite close to Pilot Iroshizuku Kon-Peki although it is a tad bit darker.
On paper, this ink behaves very nicely, with no feathering, show-through, or bleed-through. The ink is quite wet coming from my Visconti Homo Sapiens and nicely lubricates the nib. You can see some shading from a lighter blue to a darker blue, but not much. This is not one of those shading inks. The dry time is actually quite fast for a wet ink like this.
On Tomoe River paper, this ink exhibits a crazy amount of red sheen, more than any other ink I've seen before. The sheen is also present on other high quality papers like Rhodia and Clairfontaine but in lesser amounts sadly.
Here is a swab of the ink. You can see that there is a small amount of red sheen on the wetter swab on the left.
So far I have had no issues with using this ink. There is no staining at all and it is very easy to clean out of the pen.
The water test for this ink shows that it is not very resistant to water, but small traces of the color can still be found. There was not too much smearing, so it didn't impede seeing the other dry grid lines. Water was dripped into the grid for about 15 seconds then wiped off with a tissue.
The ink comes in a standard Jentle bottle with a very wide lip and a nice inkwell insert that aids in filling. Just invert the bottle the tip it back over to make filling super easy. (Photo thanks to JetPens and were used with written permission.)
Personally, I find this to be a very well-rounded and solid blue with nothing to complain about. The huge amount of sheen does set it apart from other blues within the same range. The color is dark enough to be professional but still interesting enough for letter writing and journalling.