Why Beitou Sulphur has no synthetic equivalent

Every other colour in the Yushan range has a Colour Index code, which means it's a manufactured pigment with a known chemical structure that, in principle, any paintmaker could reproduce under a different name. Beitou Sulphur doesn't have one, and the reason isn't secrecy. It's that there's no formula to protect.

What's actually in the valley

Beitou sits at the northern edge of Taipei, built around a geothermal system that has been active for thousands of years. Mineral-rich steam rises through fractured rock and deposits sediment as it cools and meets air, a slow accretion that has been mined in the area, in various forms, for over a century. The sediment isn't sulphur alone. It's a mixed mineral deposit, sulphur among iron oxides and trace metals, and the exact ratio shifts slightly from one collection point to the next.

That inconsistency is precisely what a synthetic pigment manufacturer would try to engineer out. A commercial pigment needs to be the same batch after batch, which means starting from a purified, characterized chemical rather than a variable natural sediment. Beitou Sulphur keeps the variability, because the variability is the granulation.

Why the granulation is what it is

Granulation in a watercolour happens when pigment particles are too large or too irregular to stay in even suspension, so they settle unevenly into the tooth of the paper as it dries. Manufactured pigments are ground to a controlled, fine particle size specifically to avoid this. Beitou Sulphur is ground much closer to its raw mineral state, so the particle size distribution is wide and the shapes are irregular, which is exactly the condition that produces heavy granulation.

It's also why the colour is rated semi-opaque rather than transparent. The mineral particles are large enough to scatter light rather than let it pass through to the paper and back, which is a physical property, not a formulation choice.

What "no synthetic equivalent" actually means

It doesn't mean nobody has tried to make a gold-amber granulating pigment. Several exist. It means none of them are ground from this specific deposit, so none of them granulate quite the same way under a wet-into-wet wash, the same way no two mineral deposits anywhere produce identical results. That's the whole claim, and it's checkable: put it next to any commercial mineral gold and watch how it settles.