The following letter confirms that at least the obverse head of Christopher Columbus which appeared on the 1892 Columbian commemorative half dollar was struck in cardboard.
According to Roger Burdette, "A piece of smooth faced paperboard was dampened, pressed to release excess water, then put under a soft steel die and squeezed in a small lever press (like a cheese). This produced a sharp impression with excellent detail for administrative approval.
In this instance, the squeeze went to the 3rd Asst Postmaster General because the PO wanted to use the same Columbus portrait on a stamp."
Here is what the Columbian half obverse looks like. It is believed that only the portrait was struck into the cardboard.
For a similar cardboard item, the obverse of the 1893 Isabella quarter in cardboard, the JA1893-1/P3497, click here.
The letter is from NNP's digital archive of US Mint documents. RG104 E-1 Box 178 and was supplied courtesy of Roger Burdette.
Regrettably, it is not known if the cardboard trial survived.