I had been told by the tutors of the difficulty of hemming a bias-cut dress. I was not sure exactly why it should be difficult, but on that note I made sure to work with caution and care. This is the method I devised for marking and putting up the bias hem:
First I hung the dress (by putting on a mannequin and raising it on its stand) for over a week, for I didn't want the cloth to drop more even more dramatically, distorting the shape of the hem.
I then marked the hem by putting it on my model and placing pins as markers at floor length. As mentioned before, i decided not to make the dramatic train as featured in the design of the dress, for purely practical reasons. I was very careful to work delicately with the fabric, so as not to stretch it, as obviously the hem is on the bias.
I then put the dress back on the mannequin and spread the hem across the floor, so that I could measure and check for even-ness and accuracy, and made more marks for the hem. I tacked with long stitches the position of the hem, then I trimmed the excess seam allowances to be even.
After this I took the dress to the iron and carefully pressed up the hem, giving it a very gentle steam (holding the iron up to steam above the cloth) so that the excess fullness in the seam allowance (there is excess as the pieces taper outwards) can be eased upwards to lie nicely against the body of the skirt.
I decided to give the hem a relatively wide turn-up (just over an inch) for the same reason that I used fairly wide bias-binding across the bodice: in case it rises up a little, so that the top fabric and not the backing fabric can be seen.
I then slip-stitched the hem in place. I had no real problems with the hem, hopefully due to my careful approach to it, as I was always cautious not to over-handle and stretch the fabric.