In choosing between these three scarlets, I decided to do a “what’s the difference” post!
Hue: Pyrrol Scarlet and Scarlet Lake have almost the same hue. Quin Coral is a bit more blue-toned and looks pinker, less orangey.
Opacity: Pyrrol Scarlet is semi-opaque, where Scarlet Lake is transparent. (This does not appear to be an inherent quality of the PR188 pigment, as I’ve heard DS Organic Vermilion is opaque, but the WN version is transparent.) Quin Coral is also very transparent.
Hansa Yellow Deep (PY65)
The Pyrrol Scarlet and Scarlet Lake mixes are almost identical. The Pyrrol Scarlet mix is maybe slightly, slightly duller-looking due to its higher opacity; a bit more of the white shows through in the Scarlet Lake mix. The Quin Coral makes much brighter, almost neon oranges.
Here’s another view of PR188 (top) vs PR255 (bottom) on the same sheet. In this case, I used DV Permanent Red for the PR188.
The scan doesn’t show much difference, though it’s worth noting I found the PR188 more vibrant in real life.
Quinacridone Gold (PY150/PO48)
These are all very similar. Pyrrol Scarlet and Scarlet Lake are especially near-identical. Quin Coral has a slightly brighter look, but it’s sort of hard to tell.
Ultramarine Deep (PB29)
Pyrrol Scarlet and Scarlet Lake make quite dull grayish purples, with the Pyrrol Scarlet ones being slightly duller. Quin Coral makes more vibrant, but still muted purples, that don’t get very dark.
Phthalo Blue Green Shade (PB15:3)
Pyrrol Scarlet does the best job of muting the blue – it almost makes black! The Scarlet Lake mixes were a bit washed out, and never got fully gray, remaining slightly purple. Quin Coral makes straight-up purple.
Phthalo Green (PG7)
All of these are pretty similar. I would say the most even complement is Scarlet Lake, which makes fairly even grays, while Pyrrol Scarlet’s are slightly brownish and Quin Coral’s are slightly purplish.
One note is that I found in this experiment that it was difficult to get the Scarlet Lake ones very dark, the mixes all dried fairly light.
Pyrrol Scarlet and Scarlet Lake are more similar to each other. The hue is nearly identical, and they mix very similarly. Either can be used to make bold oranges and to mute blues. I think I only need one of those two on a given palette, generally. In a vacuum, I prefer the transparency of Scarlet Lake, which helps it to feel brighter and more glowing, especially in skies. However, the opacity of Pyrrol Scarlet is preferable for some use cases; it helps it to make pop color in upper layers (for example, I’ve dropped it into tree silhouettes for a sun glow, or used it for a splash of color in a woodpecker’s head or a winter coat.) It also makes darker mixes, and more effectively mutes blues.
Quin Coral has a slightly different use case. It makes bolder mixes, generally, including bolder, near-neon oranges and vibrant purples that are closer to Quin Rose mixes than to other scarlet mixes. Therefore, it cannot be used to mute blues, because it goes purple; but the pretty purples are a boon if you want to make a lot of interesting pinky colors (e.g. botanicals).
Quin Coral is one of my favorite colors, but I have to acknowledge it’s a bit superfluous on many palettes because it covers some-but-not-all use cases of both a magenta and a scarlet. You probably don’t need it if you have both of those colors, but I also don’t feel it truly obsoletes either one. With that said, it makes unparalleled oranges and is the perfect bold coral unmixed for sunrise/sunset clouds and alpenglow!
I therefore lean toward keeping Quin Coral and if I’m going to do that, I think Pyrrol Scarlet is a better option for a second scarlet since it’s more distinct.