20. The method according to any one of the preceding claims wherein the method comprises moving the metal sub› strate such that its surface is brought into contact with the solid particles. 

21. The method according to any one of the preceding claims wherein the method comprises rotating, oscillating or reciprocating the metal substrate within the cleaning liquor. 

22. The method according to any one of the preceding claims wherein the method comprises scouring the surface of the metal substrate with the solid particles. 

23. The method according to any one of the preceding claims wherein the method comprises agitating the solid par› ticles within the cleaning liquor. 

24. The method according to any one of the preceding claims wherein the method is carried out using a fluidized bed containing the cleaning liquor. 

25. The method according to any one of the preceding claims wherein the cleaning liquor contacts the metal surface at a relative velocity of at least 1 cm per second. 

26. The method according to any one of the preceding claims wherein the multiplicity of solid particles comprises or consists of a multiplicity of polymeric particles or wherein the multiplicity of solid particles comprises or consists of a multiplicity of non-polymeric particles. 

27. The method according to any one of the preceding claims wherein the multiplicity of solid particles comprises or consists of a mixture of a multiplicity of polymeric particles and a multiplicity of non-polymeric particles. 

28. The method according to any one of the preceding claims wherein the multiplicity of solid particles comprises or consists of a multiplicity of polymeric particles. 

29. The method according to any of claims 26 to 28 wherein the polymeric particles comprise particles of one or more polar polymers. 

30. The method according to any of claims 26 to 28 wherein the polymeric particles comprise particles of one or more non-polar polymers. 

31. The method according to any of claims 26 to 28 wherein the polymeric particles comprise particles of one or more polar polymers and particles of one or more non-polar polymers. 

32. The method according to any of claims 26 to 31 wherein the polymeric particles comprise particles selected from particles of polyalkenes, polyamides, polyesters, pol› ysiloxanes, polyurethanes or copolymers thereof. 

33. The method according to any of claims 26 to 28 or any of claims 30 to 32 wherein the polymeric particles comprise particles selected from particles of polyalkenes or copoly› mers thereof. 

34. The method according to claim 33 wherein the poly› meric particles comprise particles of polypropylene. 

35. The method according to any of claims 26 to 29, claim 31 or claim 32 wherein the polymeric particles comprise particles selected from polyamide, polyester or copolymers thereof. 

36. The method according to claim 35 wherein the polya› mide particles comprise particles of nylon. 

37. The method according to claim 35 wherein the polyes› ter particles comprise particles of polyethylene terephthalate or polybutylene terephthalate. 

38. The method according to claim 26 or 27 wherein the non-polymeric particles comprise particles of ceramic mate› rial, refractory material, igneous, sedimentary, metamorphic minerals or composites. 

39. The method according to any of claims 26 to 37 wherein the polymeric particles comprise particles selected from linear, branched or cross-linked polymers. 

40. The method according to any of claims 26 to 37 and claim 39 wherein the polymeric particles comprise foamed or unfoamed polymers. 

41. The method according to any one of the preceding claims wherein the solid particles are ofhollow and/or porous construction. 

42. The method according to any of claims 26 to 37 or claims 39 and 40 wherein the polymeric particles have an average density of from about 0.5 to about 3.5 g/cm 3 • 

43. The method according to claim 26, 27 or 38, wherein the non-polymeric particles have an average density of from about 3.5 to about 12.0 g/cm 3 • 

44. The method according to any of claims 26 to 43 wherein the polymeric or non-polymeric particles have an average volume in the range of about 5 to about 27 5 mm 3 • 

45. The method according to any one of the preceding claims wherein the solid particles are reused one or more times for cleaning of metal substrates according to the method of the invention. 

46. The method according to any one of the preceding claims wherein the method comprises a step of recovering the multiplicity of solid particles after cleaning of the metal sub› strate. 

47. The method according to any one of the preceding claims wherein the cleaning formulation comprises one or more components selected from the group consisting of: sol› vents, polymers, corrosion inhibitors, builders, chelating agents, surfactants, dispersants, acids, bases, anti-oxidants, reducing agents, oxidising agents and bleaches. 

48. The method according to any one of the preceding claims wherein the method further comprises coating the metal substrate after cleaning the metal substrate. 

49. The method according to any one of the preceding claims wherein the metal substrate comprises a transition metal. 

50. The method according to any one of the preceding claims wherein the metal substrate comprises aluminum. 

51. The method according to any one of the preceding claims wherein the metal substrate is a metal alloy. 

52. The method according to claim 51 wherein the metal alloy is an alloy of iron. 

53. The method according to any one of the preceding claims wherein the metal substrate comprises a metal sheet. 

54. The method according any one of the preceding claims wherein the metal substrate is a can. 

55. A method of treating a metal substrate comprising the steps of: 

a) cleaning the metal substrate to remove contaminants according to any of claims 1 to 54; 

b) removing at least a portion of an oxide layer from the surface of the cleaned substrate. 

56. The method according to claim 55 wherein step b) comprises exposing the metal substrate to a treatment liquor comprising a treatment formulation and a multiplicity of solid particles. 

57. The method according to claim 56 wherein the method further comprises causing the solid particles and the metal substrate to enter into contacting relative movement. 

