How does "In An Artist's Studio" by Christina Rossetti convey the message of inequality between men and women in the Victorian era?
Rosetti's poem conveys not merely the unequal treatment of men and women, but how men actively objectify and dehumanize women. Under the yoke of the "male gaze" (the ogling and scrutiny of women by men), women are made into objects and in the process, lose their humanity. This logically includes their human rights.
Consider the "artist" in Rosetti's poem. While he creates the women in these paintings, he also "feeds upon her face by day and night." The artist did not create women in his art to appreciate or elevate them, but to reduce them to a few aesthetic elements and consume them. Notice Rosetti's use of diction: the man does not simply "see" the painting, but "feeds" upon the subject.
Yet art, of course, is meant to be consumed. So how do we know that the artist objectifies his female subjects? Rosetti tells us plain as day, from the very beginning of the poem: "One face looks out from all his canvasses, / One selfsame figure sits or walks or leans."
Though the artist creates many works with many different women subjects, they are all painted in a similar fashion, "one selfsame figure." This deprives the women of their individuality, their humanity. The poem makes it clear that the artist does not pay homage to women but instead manufactures a one-dimensional image of a woman for the consumption of men.
The speaker ends with the strong observation that the woman in these paintings (that is, all women under the scrutiny of men), are "Not as she is, but was when hope shone bright; Not as she is, but as she fills his dream." Rosetti criticizes this social fact of the Victorian era: that women exist solely for the comfort and convenience of men; to "fill their dreams" as opposed to having dreams of their own. Note that the repetition of "not" at the beginning of these two lines emphasizes both their importance and the negativity of the idea being addressed.
Finally, it is worth making the comparison that for a female subject to be "In the Artist's Studio" is essentially the same as being "a woman in a man's world."
This poem actually makes a number of profound statements about gender relations and also art and the depiction of women. However, you are right in identifying the gender inequality between men and women to be a key theme of this exciting and memorable poem. Key to understanding what Christina Rossetti is trying to say through this poem is the way that the woman, who is obviously the muse of the unnamed male artist, is used and abused by the painter. Note that it is "one face" that dominates all of his work, "one selfsame figure" that is depicted in a variety of different guises, whether as a "saint" or as an "angel." However, as the last few lines of the poem make rampantly clear, that all of these paintings do not show this woman in her reality, but only how she fulfils the fantasy of the artist:
Not as she is, but as she fulfils his dream.
The meaning is evident: women are not entitled to their own identity and existence. Rather, they are dependent on men to be given that identity and stereotyped reality that is really no reality at all. In a sense, we could argue that the artist/muse relationship is an allegory for the role of women in Victorian society. They only have license and independence in as much as they "fulfil the dream" of the patriarchal society in which they live, that is able to cast them in what role they wish, but always denies their own independence and reality. Women are shown only to be viewed through the male gaze that objectifies them and disempowers them.