Glassee

By means of this spell the magic-user is able to make a section of metal, stone or wood as transparent as glass to his gaze, or even make it into transparent material as explained hereafter.

Normally, up to four inches of metal can be seen through, stone up to 6-ft thick can be made transparent, and 20-ft of wood can be affected by the glassee spell. The spell will not work on lead, gold or platinum. The magic-user can opt to make the glassee apply to himself or herself only, and apply it up to once per round while spell duration lasts; or the caster can actually make a transparent area, a one-way window, in the material affected. 

Either case gives a viewing area 3-ft wide by 2-ft high. 

The material component of the spell is a small piece of crystal or glass.

The strength of the glassy area is the same as that of the original material.