Sulphur allotropes detection thresholds. Top: S₈ 5σ threshold estimation in our synthetic spectra generator. The spectrum in black contains no sulphur, while in red, where we consider that the entire cosmic sulphur abundance is locked in S₈ (see text for calculation), it still does not result in a possible detection. In teal blue, the column density needed to detect S₈ with a 5<τ threshold is an order of magnitude greater than the cosmic sulphur abundance. Bottom: Similarly to upper panel, but for the S₃ and S₄ 5σ threshold estimations (in blue and cyan, respectively). The two bands are isolated in this figure but can be seen overlapped by other features in Fig. B.3.