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Table 1 Position of the characteristic absorption bands in the reflectance spectrum and first derivative inflection points for each synthesized pigment

From: Seeing red: towards an improved protocol for the identification of madder- and cochineal-based pigments by fiber optics reflectance spectroscopy (FORS)

PigmentSubstrate (determined by FTIR)FORS features
λshoulder (nm)λabs,1 (nm)λabs,2 (nm)1st inflection point (nm)2nd inflection point (nm)
C-Std M-RAlumina, SO42−~ 495530 ± 3557 ± 1500 ± 0540 ± 1
C-Std M-Ca excessCaCO3, alumina~ 496529 ± 2560 ± 2500 ± 0540 ± 3
C-Std M-CaCaCO3~ 497530 ± 2561 ± 1501 ± 1540 ± 2
C-Std MAlumina, SO42−~ 495531 ± 2559 ± 2500 ± 0540 ± 2
C-Std M-Al ex.Alumina, SO42−, CO32−~ 494530 ± 2558 ± 2499 ± 1539 ± 1
C-SilkAlumina, SO42−, CO32−~ 496528 ± 2559 ± 1500 ± 1539 ± 2
C-FleeceProteins, alumina, SO42−~ 497529 ± 3558 ± 2502 ± 3537 ± 1
C-SnSn salt or complex~ 485520 ± 0555 ± 1501 ± 2535 ± 1
C-AlAl salt or complex~ 493538 ± 3574 ± 3503 ± 3545 ± 2
DYE15046aAl salt or complex~ 489523 ± 1562 ± 2496 ± 1533 ± 1
DYE15047aAl salt or complex~ 489526 ± 0562 ± 1500 ± 1537 ± 2
M-StdAlumina, SO42−~ 481509 ± 3~ 548 (sh)490 ± 2524 ± 1
M-Std-RAlumina, SO42−, CO32−~ 469500 ± 5~ 545 (sh)~ 488 (sh)522 ± 1
M-Std-Al ex.Alumina, CO32−~ 475500 ± 2~ 538 (sh)~ 486 (sh)520 ± 2
M-Std-CaCaCO3, alumina~ 476506 ± 0− ~ 545 (sh)487 ± 0524 ± 0
M-Std-Ca excessCaCO3, aluminand480 ± 5 (broad)~ 543 (sh)~ 487 (sh)~ 523 (sh)
M-SilkAlumina, SO42−, CO32−~ 478 (or maximum, if present)~502 (sh)~ 541 (sh, if present)~ 486 (sh)524 ± 2
M-FleeceProteins, alumina, SO24~ 478505 ± 3~ 542 (sh)488 ± 1523 ± 1
  1. The values for λshoulder, λabs,1, and λabs,2 as well as the two first derivative inflection points are averages of the values observed for the same sample across the four binding media examined. Approximate values are presented for features that are present as a shoulder and were visually identified. FTIR spectra taken for substrate characterization of all pigments can be found in Additional file 2: Figure S1
  2. sh shoulder, nd not detected
  3. aOnly painted in gum Arabic for comparison with synthesized pigments