First, I take exception to the name "frit-core" for these or any beads. It is an oxymoron. And I say this because frit is not an end-product. Frit is a substance that is produced during the process of making glass. The components of glasses are combined together and heated. Actually, roasted for hours. THAT is frit. It is typical to take frit and grind it into smaller granules, which makes the next heating come closer to melting and becoming homogenous--meaning it becomes glass. Glass components are typically roasted and ground (are "fritted") a number of times, on the way to becoming glass.
Two things have happened in the arena of glass and beads that are nonsensical:
1) "Frit" is used to characterize a certain sort of ancient beads that are (supposedly) neither faience nor glass. I have not determined who started this idea (nor when)--but it is taken-for-granted by some archaeologists. In my experience, the beads I have seen that are called "frit" are actually only glass beads that are highly-decayed and compromised. They are not some mysterious substance.
2) Among current hobbyist glass-beadmakers it has become popular to characterize ground-up glass as "frit." (Clearly, this is because actual frit is typically ground to a granular consistency.) As I have remarked elsewhere, if they would say "fritted glass" it would be slightly better. But it would still be mistaking one thing for something else.
So..., we have these obscure beads, that apparently mostly appear in fairly early horizons of North America, among trade beads, that are called "frit-core" beads. They clearly have a base (not a "core") that is composed from a granular substance. Something I would be inclined to call "composition"--and to characterize as being "faience-like." (And I would say the same thing about other similar beads, such as those from the Warring States Period in China, ca. 400 BCE, that have similar bases.) Onto this base is a glassy exterior, that is usually black with white patterns. This application seems to be rather like enameling.
I have only seen one early "frit-core" bead in real life, to actually handle it (in the collection of the archaeological museum in Montreal, Canada). However, I have seen a variety of photos of these beads; plus there is a class of glass beads that I propose were made to imitate "frit-core" beads. These are Venetian products (when their origin is not in-doubt). So, these beads are recognizable and distinguishable.
Who made "frit-core" beads? This is anyone's guess. But I'm inclined to suspect they are European, and perhaps French. I suggest France mainly because they have a history of making products from pate de verre ("glass paste"). But, I suppose there may have been other industries in which non-traditional (not-hot-working) techniques were employed in glassworking. Northeastern North America is also a region where French fur-traders were active from Early Contact times (the 16th C.).
I could go on about glass paste or powderglass, and its exploitation, but it would be beside the point here. (This would include Native American-made powderglass beads; and West African powderglass beads.)
So let's turn to India. In India there is a class of beads that are conventional wound glass products, that are decorated with powdered glass. (What some current glassworkers refer to as "frit.") They have a flat, probably metal, board that has recessed patterns engraved into it. And powdered glass is used to charge these recesses (and the excess is carefully wiped-away). A hot wound bead, still on its mandrel, is rolled over the pattern glass, that then sticks to the bead and becomes its decoration. This is a strategy that is exploited by industries wherein the workers are not skilled at conventional trail decoration. It is "better than nothing" but not impressive.
The above are the only beads I know of (or can think of) from India, that involve a powdered glass component. But this is the outside--and not the inside. So, why would India be a candidate for having made "frit-core" beads? I understand that beads-de is remarking that the beads discussed are thought to be "imitations" of "frit-core" beads —and therefore need not be "the same" as "frit-core" beads. But the primary question remains--why India?
By the way, the colorful bead shown by beads-de, in his/her companion post, would be the only such bead I have seen that is not white-on-black. But, viewing the photo, it does appear to have a composite interior. Very interesting.
these oval-ish beads appear to me to resemble fairly recent furnace-wound beads from India with decoration designs of lines and dots on the surface created not with canes of molten opaque glass but more like patterns of granules in contrasting white - carefully spread on the (metal) working table surface and picked up by the bead before the glass cools and solidifies. will look for images of similar...
However, I have not seen these particular beads from that industry. Plus the decoration is not quite, visually, what I would expect to see. A closer view might be helpful.