To calibrate a printer

1. A method to calibrate a printer, the method comprising:

controlling printing of at least one layer of white ink on a substrate, the at least one layer of white ink having an opacity of at least 55%;

controlling printing of a layer of non-white ink on the at least one layer of white ink;

receiving data for at least one sensed variable of the non-white ink; and

calibrating the printer using the received data for the at least one sensed variable of the non-white ink.

2. A method as claimed in claim 1 , wherein the at least one sensed variable of the non-white ink includes at least one of: thickness of the layer of non-white ink; optical density of the layer of non-white ink; and color density of the layer of non-white ink.

3. A method as claimed in claim 1 , wherein the substrate is one of: a metallic substrate; a substrate having a relatively glossy surface; a non-white substrate; a transparent substrate.

4. A method as claimed in claim 1 , further comprising:

controlling printing of at least one layer of non-white ink on the substrate;

controlling printing of a layer of white ink on the layer of non-white ink;

receiving data for at least one sensed variable of the white ink; and

calibrating the printer using the received data for the at least one sensed variable of the white ink.

5. A method as claimed in claim 4 , wherein the at least one layer of non-white ink is at least one layer of black ink.

6. A method as claimed in claim 4 , wherein calibrating the printer includes calibrating dot gain of white ink.

7. A method as claimed in claim 1 , wherein the method is performed automatically and without user intervention.

8. A method as claimed in claim 1 , wherein the substrate selected from a group of substrates consisting of: a metallic substrate, glossy surface substrate and a non-white substrate.

9. A method as claimed in claim 1 , wherein the at least one layer of white ink is printed directly on and in contact with a surface of the substrate and wherein the layer of non-white ink is printed directly on and in contact with a surface of the at least one layer of white ink.

10. A method as claimed in claim 1 further comprising:

controlling printing of a second layer of non-white ink on the at least one layer of white ink, the layer of non-white ink having a first color and the second layer of nonwhite ink having a second color different than the first color;

receiving data for a sensed characteristic of the second layer of non-white ink; and

calibrating the printer using the received data for the second layer of non-white ink.

11. A method as claimed in claim 10 further comprising:

controlling printing of at least one layer of non-white ink on the substrate;

controlling printing of a layer of white ink on the layer of non-white ink;

receiving data for at least one sensed variable of the white ink; and

calibrating the printer using the received data for the at least one sensed variable of the white ink.

12. An apparatus to calibrate a printer, the apparatus comprising:

a controller to:

control deposition of white printing material on media, the white printing material having an opacity of at least 55%;

control deposition of non-white printing material on the white printing material;

receive data for at least one sensed characteristic of the non-white printing material; and

calibrate the printer using the received data for the at least one sensed characteristic of the non-white printing material.

13. An apparatus as claimed in claim 12 , wherein the at least one sensed characteristic of the non-white printing material includes at least one of: thickness of the layer of non-white printing material; optical density of the layer of non-white printing material; and color density of the layer of non-white printing material.

14. An apparatus as claimed in claim 13 , wherein the media is one of: metallic media; media having a relatively glossy surface; non-white media; transparent media.

15. An apparatus as claimed in claim 12 , wherein the controller is to:

control deposition of non-white printing material on the media;

control deposition of white printing material on the non-white printing material;

receive data for at least one sensed characteristic of the white printing material; and

calibrate the printer using the received data for the at least one sensed characteristic of the white printing material.

16. An apparatus as claimed in claim 15 , wherein the controller is to calibrate dot gain of white printing material using the received data for the at least one sensed characteristic of the white printing material.

17. An apparatus as claimed in claim 12 , wherein the controller is to function automatically and without user intervention.

18. An apparatus as claimed in claim 12 , wherein the controller is to further:

control deposition of a second non-white printing material on the white printing material, the second non-white printing material being different than the first non-white printing material;

receive data for least one sensed characteristic of the second non-white printing material; and

calibrate the printer using the received data for the least one sensed characteristic of the second non-white printing material.

19. A non-transitory computer-readable storage medium encoded with instructions that, when performed by a processor, cause performance of:

control printing of at least one layer of white ink on a substrate, the at least one layer of white ink having an opacity of at least 55%;

control printing of a layer of non-white ink on the at least one layer of white ink;

receive data for at least one sensed variable of the non-white ink; and

calibrate the printer using the received data for the at least one sensed variable of the non-white ink.

20. A non-transitory computer-readable storage medium as claimed in claim 19 , encoded with instructions that, when performed by a processor, cause performance of:

control printing of at least one layer of non-white ink on the substrate;

control printing of a layer of white ink on the layer of non-white ink;

receive data for at least one sensed variable of the white ink; and

calibrate the printer using the received data for the at least one sensed variable of the white ink.