Treatment of materials refers to the transformation of the essential properties of an object, a substance or a material through mechanical or chemical processes that render that object, substance or material quantitatively or qualitatively different than they were before the treatment or transformation. For example, the tanning of leather makes the final product so different from the original material (raw leather) that it may be considered an entirely new product. It is worth mentioning that Class 40 also covers the treatment of intangible materials and so services such as air purification are also in this class.
"Custom assembling of materials for others" is a key service in Class 40. The transformation of leather, thread, rubber, metal and, perhaps, plastic into a shoe is a treatment of those materials to the extent that the final product is different from any one of its components. This extends to the custom production of food and beverages, such as beer brewing or custom manufacturing of bread. However, for such transformation to be considered a service, it must be performed for the account of others (see the Explanatory Note of Class 40). It should be noted that services relating to the preparation of food and drink for immediate consumption belong to Cl. 43, however.
It is worth bearing in mind that activities such as cleaning, maintenance or repair of an object are not considered to be "treatment of materials" since they do not alter the physical or chemical properties of the object but, rather, return the object to its original condition or preserve it without changing its essential nature. Cleaning, maintenance and repair services are thus in a different class, namely, Cl. 37.