One-Way Glass is a new item added by the Secret Rooms mod. It uses Camoflage Paste [sic] in crafting.
Crafting[]
Shapeless
The Camoflage Paste [sic] can be along the top, left, bottom, or right sides with glass filling in the other 6 spaces to obtain 9 One-Way Glass blocks. This recipe is not completely shapeless.
When placed, it takes on the texture of the block it was placed on, but only on the side you placed it from. On the other side, however, you can see through it like glass. This is excellent when creating secret bases.