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

Table 6

Color change measurements of blue and red stamps compared with unprinted papers before and after photoaging.

Paper sample	Treatment	∆L		Δa		Δb		ΔE
		B	A	B	A	B	A
Unprinted paper samples	Blank	83.91	81.60	0.79	0.17	5.17	9.9	5.30
	TiO2 NP	83.94	83.91	0.57	0.52	5.13	7.38	2.25
	Klucel G	87.37	86.86	0.72	0.51	5.11	7.50	2.45
	Klucel G + TiO2 NP	87.51	87.49	0.79	0.78	5.44	7.52	2.08
Blue color stamp	Blank	17.11	20.32	0.64	1.59	7.11	8.59	3.66
	TiO2 NP	27.05	28.48	1.94	2.28	11.96	12.56	1.59
	Klucel G	19.25	21.89	1.38	2.13	9.85	10.88	2.93
	Klucel G + TiO2 NP	20.99	21.89	1.55	1.81	10.21	10.64	1.03
Red color stamp	Blank	36.47	33.99	37.20	35.69	12.53	8.94	4.62
	TiO2 NP	36.59	34.89	29.79	28.62	8.44	6.38	2.92
	Klucel G	39.52	37.48	30.94	29.52	9.01	6.39	3.61
	Klucel G + TiO2 NP	37.98	37.67	30.68	30.42	6.81	5.01	1.84

B : before ageing; A : after ageing.