387. When a person has made use of materials which in part belonged to him or her and in part did not, to make a thing of a different kind, without either of the 2 materials being entirely destroyed, but in such a way that they cannot be separated without inconvenience, the thing is common to the 2 owners, in proportion, as respects the one, to the material belonging to him or her, and as respects the other, to the material belonging to him or her, and to the price of the workmanship.