I enjoy trying to date old photographs by the clothing and hairstyles of the people in them. The best indication on this one is the shape of the young woman's large bishop sleeves, with upper arm fullness set under bretelles. This style is first mentioned in the fashion magazines in 1858.
The dress is probably silk taffeta and has the very wide lace collar popular throughout the 50's, but which was not worn in the next decade.
I can't tell whether the skirt is gathered or cartridge-pleated onto the bodice but it certainly worn over a hoop and several petticoats.
The woman's hair is done in the style of the late 50's, with broad side poofs (I would bet they are supported by switches of fake hair underneath)and a coiled bun low on the back of her head.
She looks very stylish, so I think the dress is a new one for the portrait, not one that is several years old. I'd put the date at 1858 or 59.
Andrew - if you know the date of the photograph, please tell me if I got close with my guess.
I would be very worried about the image fading from the glass. Is there any way to make a copy of the photo for framing so the customer could put the original in a dark place?
Kit