Stained framed glass that has different patterns for the frame (Example from Jerm's Vanilla Edits) : r/QuarkMod
FORGE] [1.4.7] [UPDATED] The Spy Glass Mod, SNEEKY 1 WAY GLASS ! UPDATED AND AWESOME! - Minecraft Mods - Mapping and Modding: Java Edition - Minecraft Forum - Minecraft Forum
General Layman's Aesthetic Spying Screen Mod 1.12.2 (GLASS) - 9Minecraft.Net