
A single pigment, transparent red-brown. (I am constantly misidentifying this as ‘Quinacridone Burnt Sienna’, so I’m lucky there is no color by that name.)
Experiment Results
Gradient: A lovely even smooth gradient from a deep red-brown to a light red glaze (not pink, not orange, not peach). Moderate tinting strength; difficult to get extremely dark.
Opacity: Transparent.
Granulation: Not granulating.
Glaze: Deep brown glaze, darker than the masstone I was able to achieve.

Salt: Moderate reaction
Droplets: Strong reaction
Comparison to Other Colors
Daler Rowney – Perylene Maroon

Daler Rowney’s Perylene Maroon is a similar hue, but QBS is a bit more orange.
Color Mixes
Nickel Azo Yellow

I got a much deeper color out of QBS than I usually can on the end of this gradient; I think I got a chunk of dry paint stuck on my brush! This is not typical.
These mixes look nice to me; a classic Quin Gold hue. Some companies do use a PY150/PR206 mix for their Quin Gold!
Transparent Brown Oxide

The middle brown hue of TBO pulls QBS into the mahogany brown space.
Carbazole Violet

A muted sunset combo, with mixes in the dull maroon area. A bit muddy.
Prussian Blue

Nice muting of Prussian Blue to blue-gray, and QBS to dark maroon. The middle tones are dull browns, not gray.
Cerulean

Now here are some nice grays, with interesting flecks of bright blue granulation!
Phthalo Green

It feels like these are close to, but not quite complements. Or perhaps it’s possible to get an even gray, but I just didn’t manage it. Muddy mixes in my eyes.
What Others Say
Made with PR206, this can replace Brown Madder in many palettes, or provide a transparent alternative to Indian Red. It is also a convenient colour to use for shadows in scarlet flowers.
Jane Blundell
TOP 40 PIGMENT Quinacridone maroon PR206 is a lightfast, semitransparent, moderately staining, dark valued, moderately intense earth red pigment… a very attractive color for botanicals, portraits, or landscapes. It is an unusually versatile neutralizing complement with a wide range of blue and blue green pigments, from iron blue (PB27) to viridian (PG18). It adds a slight granular texture to the phthalocyanines and complements the granular texture of the cobalts; it creates evocative dark mixtures with dioxazine violet, hansa yellow, and indanthrone blue. Its major drawback is its relatively weak tinting strength; other dark pigments can overpower it; for that reason I prefer perylene maroon (PR179). An excellent glazing pigment to cut the saturation of cool hues or to build warm shadows; very easy to handle overall. See also the section on quinacridone pigments.
Bruce McEvoy
My Review
I like this a lot! I often like my earth colors to be granulating, but the transparent non-granulation of this one makes it a lovely smooth mixer. I much prefer its mixes to those of Perylene Maroon. They both mute cool colors (making, say, blue in to blue-gray), but Perylene Maroon does so in a way that I find muddy and ugly and Quin Burnt Scarlet does so in a way that I find natural and beautiful. (I bet most people wouldn’t see any difference at all, and it may all be in my head, but that’s where I live, so.)

I also prefer this to Indian Red/Lunar Red Rock, which have an opacity that I find quite harsh.
As McEvoy notes, this has a slightly lower tinting strength than I would ideally like which makes it a bit difficult to mix with high-strength colors like Phthalos. However, its superior color and mixes (to me) make it my red-brown of choice.
That said, I don’t think red-brown is a must-have color for me, generally; though I like it for a larger palette with extended earth tones.