Day 4 is Polar Glow, a sheening ink. Nitrogen is the best match for the sheen, but Blue Water Ice is a slightly better match for the color.
The photo below is provided to showcase the sheen.
The large brush swab and horizontal writing sample in the center is the Inkvent ink. Below the Inkvent swab, I’ve swabbed each Dupe ink twice: heavily (to show shading) on the left, and lightly (no shading) on the right. Above the Inkvent ink writing, I’ve written with the dupe ink.
All swabs were created with a small paintbrush, and all writing was with a Zebra G dip nib.
I want to remind you that I can’t guarantee that the color you see on your screen will be true to life. However, I’ve put all the dupes on the same page, and scanned/photographed them together. So any differences in color will show equally across all of the inks. You’ll see how the colors look in relation to each other, which is the main point of these posts.