phone case- printing with black color on white background leave some dirt/mark

[davidlionardy]

hi , i usually use default setting to print my phone case , lately i try the photo and best photo setting on my epson R230 . it give great result . but when it print on my case , the black ink seems to leave some mark / dirt ( i dunno how to say , english is not my primary language ) .





any idea why is thing happening? . thank you in advance