Method of minimizing absorption of visible light in ink compositions comprising infrared metal-dithiolene dyes

1. A method of minimizing absorption of visible light in an ink composition comprising an IR-absorbing metal-dithiolene dye, wherein the dye is preselected from a metal-dithiolene of formula (II):

wherein:

M is selected from Ni, Pd or Pt (preferably Ni);

j is selected from 1, 2, 3 or 4;

k is selected from 1, 2, 3 or 4;

n is 0, 1, 2 or 3;

W is selected from: a substituent comprising an ammonium group; a substituent comprising an acid group, including salts thereof, or a substituent comprising a sulfonamide group;

up to three −(CH 2 )— groups in the carbocycle are optionally replaced by a group independently selected from —C(O)—, —NH—, —S—, —O—;

up to three —CH— groups in the carbocycle may be optionally replaced by —N—; and

up to four H atoms in the carbocycle may be optionally replace by a group independently selected from C 1-6 alkyl, C 1-6 alkoxy, C 5-12 aryl, C 5-12 arylalkyl, halogen, hydroxyl or amino.

2. The method of claim 1 , wherein M is Ni.

3. The method of claim 1 , wherein j is 1 and k is 2.

4. The method of claim 1 , wherein said dye comprises a —C(C 1-4 alkyl) 2 -bridging group.

5. The method of claim 1 , wherein n is 1.

6. The method of claim 1 , wherein W is a substituent comprising a group of formula —CO 2 Z, —SO 3 Z, —OSO 3 Z, —PO 3 Z or —OPO 3 Z, wherein Z is H or a water-soluble cation.

7. The method of claim 6 , wherein W is of formula —(CH 2 ) t —SO 3 Z, wherein t is 0 or an integer from 1 to 6, and Z is H or a water-soluble cation.

8. The method of claim 6 , wherein W is of formula —CH 2 SO 3 H, —CH 2 SO 3 Na or —CH 2 SO 3 K.