Student or Learner
1) Designer clothings are considered as artistic product.
2) This shoe is an art/ an artistic product.
Regardless of whether I agree with the statements and only from a grammatical point of view, I would say, "Designer clothes are an artistic product" or "Designer clothes are artistic products." The difference is whether you want to consider "designer clothes" as a compound noun or "designer" as an adjective and "clothes" as the noun. Either is OK. In your second example, the statement should be "This shoe is an artistic product".