Juxtaposed with 'Melia's "fair garments" and pretty face is all the dirt and grime associated with country life, the life 'Melia used to have and which the other woman likely still has. Just as the clothes symbolize 'Melia's new social status and life, so the dirt and grime of the country symbolize poverty, hard labor, and all kinds of other stuff associated with the laboring class. While lots of Victorians, and many other writers before them, idealized country life, in this poem Hardy reminds us of its grim realities.
Line 5: 'Melia's shoeless feet and "tatters" symbolize the impoverishment of her life on the farm (the "barton") and also how far she has come since then.
Line 6: We get no specific references here, but we can't imagine that digging ("spudding") for potatoes is clean work. Again, this is a symbol for the dirty, back-breaking work of the country.
Lines 9-10: Here, we get some metaphorical dirt, in the form of the phrases "'thik oon'" and "'theäs oon'." If you say these out loud, it almost sounds like gibberish.
Line 12: "Polish" here is a metaphor for the fact that 'Melia has stripped away all the dirty of her previous life, all the "tatters" and dialect words and grime of the country.
Line 13: 'Melia's "paws" and "blue and bleak" appearance also symbolize the ravages of country life on the body. We can't help thinking of 'Melia's "paws" as black hunks, or her face as a slightly darker color from being out in the fields all day.
Lines 23-24: 'Melia's friend is a "raw country girl." "Raw" is a metaphor for the woman's social status (an uneducated, dirty country laborer), and it contrasts with 'Melia's own metaphorical description of herself as "polished."