Every Hebrew scroll I've ever seen has been written on only one side. This makes sense both due to the physical properties of velum (the outer side is smooth and easy to write on; the inner side is rough and hard to write on) and because it would be hard while reading a scroll to "flip it over" and read on the opposite side.
But Revelations 5:1 mentions a "scroll written on the inside and on the back" (NASB). I realize that the book of Revelations itself is out-of-scope for this community, but I'm wondering if anyone here can shed light on the historical Jewish context of this passage. Were Hebrew scrolls really ever written on both sides of the velum? And if so, were there any special preparations made to the velum to facilitate writing on the rough side? And under what circumstances would these two-sided scrolls be used?