Arsenic is a semi-metallic element that poses a number of challenges conspiring against this cube becoming a commercial reality. For starters, since it’s not metallic it can’t be made by the same process as the rest of the cubes which all rely on a carving stylus working against an electrically conductive piece. While arsenic is weakly conductive the problem is that the stylus also requires being immersed in water during the process. This work environment would only serve to instantly shatter the piece of arsenic and then its shards to quickly oxidize into poisonous arsenic trioxide.
The alternate method involves a lot of manual work. Plan B calls for the element to be crushed into powder under an inert gas to prevent oxidation then agglutinated with a binder to give it structural strength. Once clumped into a solid it can then be sliced into the rough final form after which it goes through a precision grinding final step to get it to the strict cubic centimeter dimensions.
The last touch is to spray it with a thin coat of sealant to both prevent further oxidation as well as ensure low toxicity so that it can be handled with bare hands. However, arsenic can only be made comparatively safe to handle lightly. It is a toxic element which can cause serious harm if accidentally ingested or allowed to be broken up into small pieces which can become airborne and breathed in. Treat it with care and you will have about as exotic a collectible as one can imagine!