The persona that Plath creates in this wonderful poem is shown to speak in a tone that perfectly represents its character. The mirror tells us that it is "silver and exact," and it seems to speak in a rather clinical voice that presents its view as being somewhat detached and completely unemotional. This can be shown through the short sentences and the very matter of fact way in which the mirror reports to us what it sees:

I am silver and exact. I have no preconceptions.
Whatever I see I swallow immediately
Just as it is, unmisted by love or dislike.

There is therefore almost a clinical tone to the way in which the mirror speaks and how it describes the woman that spends so much time looking into it. There is no pity or sadness expressed through the speaker's tone, only a factual and unemotive reporting of what happens.