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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)

Pigment

Substrate (determined by FTIR)

FORS features

λshoulder (nm)

λabs,1 (nm)

λabs,2 (nm)

1st inflection point (nm)

2nd inflection point (nm)

C-Std M-R

Alumina, SO42−

~ 495

530 ± 3

557 ± 1

500 ± 0

540 ± 1

C-Std M-Ca excess

CaCO3, alumina

~ 496

529 ± 2

560 ± 2

500 ± 0

540 ± 3

C-Std M-Ca

CaCO3

~ 497

530 ± 2

561 ± 1

501 ± 1

540 ± 2

C-Std M

Alumina, SO42−

~ 495

531 ± 2

559 ± 2

500 ± 0

540 ± 2

C-Std M-Al ex.

Alumina, SO42−, CO32−

~ 494

530 ± 2

558 ± 2

499 ± 1

539 ± 1

C-Silk

Alumina, SO42−, CO32−

~ 496

528 ± 2

559 ± 1

500 ± 1

539 ± 2

C-Fleece

Proteins, alumina, SO42−

~ 497

529 ± 3

558 ± 2

502 ± 3

537 ± 1

C-Sn

Sn salt or complex

~ 485

520 ± 0

555 ± 1

501 ± 2

535 ± 1

C-Al

Al salt or complex

~ 493

538 ± 3

574 ± 3

503 ± 3

545 ± 2

DYE15046a

Al salt or complex

~ 489

523 ± 1

562 ± 2

496 ± 1

533 ± 1

DYE15047a

Al salt or complex

~ 489

526 ± 0

562 ± 1

500 ± 1

537 ± 2

M-Std

Alumina, SO42−

~ 481

509 ± 3

~ 548 (sh)

490 ± 2

524 ± 1

M-Std-R

Alumina, SO42−, CO32−

~ 469

500 ± 5

~ 545 (sh)

~ 488 (sh)

522 ± 1

M-Std-Al ex.

Alumina, CO32−

~ 475

500 ± 2

~ 538 (sh)

~ 486 (sh)

520 ± 2

M-Std-Ca

CaCO3, alumina

~ 476

506 ± 0

− ~ 545 (sh)

487 ± 0

524 ± 0

M-Std-Ca excess

CaCO3, alumina

nd

480 ± 5 (broad)

~ 543 (sh)

~ 487 (sh)

~ 523 (sh)

M-Silk

Alumina, SO42−, CO32−

~ 478 (or maximum, if present)

~502 (sh)

~ 541 (sh, if present)

~ 486 (sh)

524 ± 2

M-Fleece

Proteins, alumina, SO24

~ 478

505 ± 3

~ 542 (sh)

488 ± 1

523 ± 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