Hi Erik, thanks for the answer.
I shoot with black ground and two light in front of object.
for pattern i draw to the surface , you said “not anything strange” . i still not sure why my drawing cause that noise , you know some models in sketch fab also has various color in their surface , but their model detail is perfect , why my drawing to surface cause constructed mesh ugly ? how should i judge which model with kind of color in their surface should use spray for that kind of model , confuse a bit.