Characterization of Two Historical Postage Stamps Made from Cotton Fibers and Their Restoration Trials Based on the Experimental Studies

Table 4

Similar functional groups to the FTIR spectrum of the blue and red stamps in linseed oil medium sample.

Functional group	Wavenumbers (cm^-1)
	Standard linseed medium	Linseed oil reference spectrum	Blue stamp sample	Red stamp sample
O-H stretching band	3200–3600	—	3281	3305
C-H stretching bands (methyl and methylene groups in triacylglycerol molecules)	2800–3000	2865–2927	2851–2920	2851–1919
C=O stretching (triglycerides (esters, fatty esters and carboxylic acids))	1500–1750	1745	1643–1789	1578–1642
C-H bending bands	1300–1480	1426	1406	1414
C-O stretching bands	900–1300	1168	1003	983–1065
C-H torsion	700–750	727	711	—

Data are from [17, 86]. Standard linseed oil.