Is there a difference - coin dot, spot optic, inverted thiumbprint ?

So far, my impression is that coin dots are very defined circles within the body of the glass, more-so than optic spots or thumbprints, inverted or not.
Clearly a lot of web sellers very loosely use as many terms as possible to get search hits.

I have a glass piece and I can feel the indentations on the inside but not on the outside. They are quite subtle, certainly not a polka dot effect, not a colour variation but an integral part of the glass, like a thumbprint.





I'll try and show a photo.
I have other questions about this piece I think I should save for a separate thread.
Well, thanks in advance for any help.

 

I can't help, but others will be along who can.

 

I'm probably not the best to answer this, I'm biased.

When the effect was begun, ca. 1884, it was called Polka Dot. Early researchers ca. 1925 didn't know this and named it "inverted thumbprint." As if a thumb could imprint glass and survive to make the second imprint. Within a year or two of its introduction the opalescent process became involved and we had white polka dots on a colored ground. I would call these opalescent polka dots. Within the next five years, (before 1890) uncolored circles within colored ground had been developed. The manufacturers simply called these Opalescent Wares.

Since I seem to be a traditionalist, I see no reason to invent names for them, they have names their makers applied to them. Also, I don't expect their size would influence their name, but I suppose "tiny" and "giant" could be added.

Fenton seems to have called their wares something, I guess their names could be used, too, but I haven't kept up with the new manufacturers.

 

I think it was unfortunately named originally then, simply because I believe for most today the term "polka dot" implies different colours, absent any optical effect. It certainly does for me.

That said, I tend to favour tradition & don't like goofy names meant only to hype something up !

To me, "coin spot" suggests a mark impressed upon a piece in a precise circle, whereas "thumbprint" also suggesst impressing but with irregularity.

BUT - in the piece I have, the interior indentations are so regularly spaced that looking through to the light one sees an effect like looking through fish-netting!
Very uniform but soft-edged rather than with a linear definition.

I've found it extremely difficult to photograph, but I love the effect !
I'll start a thread for identifying that piece & hopefully have some decent pics.

 

The term "Polka Dot" first appeared published in the English Language in 1883 (OED) in reference to a pattern if fabric. Yes, it was color differentiation. I suspect the name/phrase was popular and became readily applied to anything close.