This mid 1800s plate I believe is wedgwood Blue and white Marbled. Later pieces had a backstamp this one has a impressed crown mark the diamond is there but I can not make out the impressions in it, it also as an impressed X. The plate has staining as shown, but no chips that I noted. The staining is worse on one area hard to picture,but it's darker as noted. The back also has some staining. But this plate is nearly 175 years old. so let's cut it some slack. Very hard to find pattern. Measures 10 inches