Just added it to the Stardew Valley Wiki. The wallpaper 72 has the same ID as a Diamond, so technically, it could produce infinite diamonds if put in a Crystalarium. The following wallpapers should also work: 60: Emerald, 62: Aquamarine, 64: Ruby, 66: Amethyst, 68: Topaz, 70: Jade. 72: Diamond, 80: Quartz, 84: Fire Crystal
Bit of a necropost. The exploit for the dinosaur and galaxy sword was found, but not the one for the crystallarium, if I'm not incorrect.