I found one more reference to these tiles, from an old ebay auction on picclick (https://picclick.com/6-Antique-Textured-Cupboard-Sun-kissed-purple-late-303540929418.html):
Take a look at these Sun kissed purple late 1800s manganese dioxide glass panes.
These industrial panes measure
5”X5”x1/4”
And are marked
RICE’S ARISTO
with embossed letters.
These panes are where made to be used with lead seams.
I have quite a few of these beauties.
The original auction and its pics are long gone but picclick (https://picclick.com/6-Antique-Textured-Cupboard-Sun-kissed-purple-late-303540929418.html) still has this thumbnail saved:
(http://glassian.org/Prism/rices_aristo_tiles.jpg)
Looks like a duck. I'm 99% sure these were in fact ducks (prism tiles). 4"x4" was the common size, but there were also 5"x5". What RICE's ARISTO means is still uncertain, and the toy/sample washboard just muddies the water. It does look just like the typical washboard of the time, right? The following is 18" x 7-3/4" x 1-1/4"
(http://glassian.org/Prism/glass_washboard.jpg)
And here's another:
(http://glassian.org/Prism/glass_washboard2.jpg)