I have only recently become aware of this, but MEMRI reports that the gentlemen from the Islamic State have been considerate enough to put out a pamphlet which describes, in question and answer form, the rules for the enslavement of women:

It is, of course, permissible to have intercourse with one’s property, although in the West – due to our racism – we tend to think of such arrangements as rape… but what do we know? Besides, as Obama has pointed out, it’s all relative. I mean, sure the Islamic State buries children alive, but there was the Crusades, so get off of your high horse.
You should know, if any of you guys decide to join up, that it is not permissible to sell, and thereby separate, a pre-pubescent girl from her slave mother. It is only when she passes the age of pre-pubescence – usually around the age of thirteen – that it is permissible to sell or otherwise dispose of such a slave.
So, please, do not think that there are no rules. There are rules and I do not think that I have to remind you how the Islamic State deals with people who violate their terms.
It is also impermissible for a master to have intercourse with his slave if he does not own that slave exclusively. In other words, if Jay and I were to join up and pool our resources to purchase a slave girl, it would be impermissible for either of us to intimately enjoy the young lady’s company. Likewise, if either of us were to marry a Muslim woman, it would be forbidden for us to have intercourse with one of the wife’s slaves, because the slave would not be our exclusive property.
Furthermore, if you get one of your slaves pregnant and she has a baby it is then forbidden to sell her… which I think is a bit intrusive of property rights and should probably be rescinded, but, sadly, it is not up to me.
The rules on the dress of female sex slaves is a bit more liberal than you sometimes find elsewhere among the deeply spiritual. She may allow her feet and hands to be uncovered, as well as her neck and her entire head so long as their is no enticement of men happening. If there is then, apparently, she must be covered from head to toe in a potato sack and allowed, basically, to hop around the house.
It is permissible to beat one’s slaves, of course, but even here there are limits to property rights. You may beat your female sex slaves, but only for purposes of discipline, never for the sheer fun of it… which, as far as I am concerned, takes all the fun out of it.
In any case, I want to thank the gentlemen of the Islamic State for clarifying their rules on such matters. I know that after they conquered the Yazidis and chopped off a bunch of heads and buried people alive, and so forth, some of the guys were concerned about the Islamic rules for their female sex slaves and the document above lays it out in a readable and accessible manner.
Now you know.