Fig. 2

a Poliergold models with yellow and red bole substrates including (from top to bottom) “y4_pg”, “r1_pg” and “r5_pgx2”; b Doppelgold models with blue-grey bole substrates including “b1_dg”, “b4_dg” and “b2_dgx2”; c Doppelgold models with yellow and red bole substrates including “y7_dg”, “r7_dg”, “r9_dg” and “r10_dgx2”; d Doppelgold models including the ground gilding model “w1_dg” and the oil gilding model “w4_dg_oil”; in the latter a gold size layer is located between the white ground and gold leaf, and thus invisible in the image; e bare substrates including yellow bole, red bole, blue-grey bole and white ground. The dark areas in the gilded sections of some models are the reflection of the camera lens