Sepia Black is one of the six colors in Platinum's new Classic Line of iron gall inks. The press release for the Classic Line says that Platinum focused on the color change "with the aim to enhance the joy of using fountain pens." They also tried to emphasize shading to offer rich writing. Each of the colors are intended to write a bright color and then gradually darken to black.
Initially, I wasn't interested in this particular color; however, I ordered several other things from Vanness, and they very kindly sent me a free sample of Sepia Black. So, after reviewing Cassis Black and Lavender Black, I inked up a pen with Sepia Black...and it was green! I checked the bottle; no, I wasn't imagining things, it was Sepia Black. I squinted - still green. I flushed the pen, cleaned it, and refilled it - still green. I looked at some other brown things to make sure I could still see brown - I could (that was a relief). Then I looked at the Platinum site; I should have started with that because it seems that Sepia Black starts out green. The olive green color showing the nib sizes next to the bottle is a reasonable accurate representation of what this ink looks like wet.
The color change on Sepia is slow; I didn't notice anything until the next day, and anything closer to brown than green took several days. The review, Rhodia, Clairefontaine, and Tomoe River pages have all been finished for about a week. The other samples have had about 4 days to darken. So far, none of them have gotten to the rich brown of the swab under the bottle in the Platinum promotional material. I can still see green undertones in most of them, especially on the Tomoe River. I think the nicest browns are on the Clairefontaine Triomphe with the Pilot 92 & the TWSBI Eco B and also on the Original Crown Mill Laid Paper with a glass dip pen; however, this is a matter of personal preference.
There is a lot of color variation between pens and paper, which also occurred with Cassis and Lavender. I experimented a bit with different papers (and one not-paper paper - the Ogami Repap Stone Paper, which is ground limestone with plastic as a binding agent) and a glass dip pen. These are all papers I actively dislike, but I thought maybe they could provide some insight on the color variation (since they range from high quality and super absorbent to low quality and absorbent to not at all absorbent). They did not provide any insight except that the OCM LP seems to darken more than the others.
Somehow I left the Saturation and Water-Resistance blank in the review. I know the WR is because I was waiting for the test to dry; it performs well in a drip test. As for the Saturation, maybe it was unconscious; the variation between pens and papers makes it difficult to rate. On average, I'd say it's a medium-high saturated ink.
Rhodia Writing Samples
Clairefontaine Triomphe Writing Samples
Tomoe River Writing Samples
Various Writing Samples, including Original Crown Mill Laid Paper and Pure Cotton, Ogami Repap Stone Paper, cheap office notepad, and generic copy paper. (I mislabeled the notepad and the copy paper - the pen was a TWSBI 540, not a 580.)