Good questions!
Clays are compression molded, not injection molded. It's one of the defining features of clays.
However, there are a lot of chips that are marketed as "clays" or sometimes "clay composites" which are completely unlike clays. There are no official standards as to what "clay" means, so as a marketing term it's meaningless.
Around here, we categorize chips more-or-less like this:
- Clays, which are compression-molded and have inlays pressed into the chip
- Ceramics, which are injection-molded and are printed on directly using dye sublimation
- Plastics, which are injection-molded and have adhesive labels stuck onto the chip
... even though all three are actually made out of plastic. Because of the different plastic formulas, the "clay" chips kinda look and feel like actual clay, and the "ceramics" kinda look and feel like actual ceramic (including making a "clink" sound).
Quality is subjective. It's more appropriate to say that each manufacturer chooses the materials for their chips in order to give them the characteristics that they want, and then we the consumers decide what we think the quality of the final product is. Most people think clays are the best-feeling chips and slugged chips are the worst, but that's only partly because of the materials. The way they're manufactured has a lot to do with it as well.
Mass-market slugged plastics such as dice chips are made to be low-cost, so they use cheaper materials, simpler manufacturing processes, simpler molds, and less quality control. High-quality casino-grade slugged plastics such as Matsui, Abbiati, and Bud Jones use more expensive materials, more complicated manufacturing, more complicated molds, and a great deal of quality control.
Clay chips are compression-molded, which is a very labor-intensive process. Ceramics are somewhere in the middle; the blanks are injection-molded so are cheap, but the printing is labor-intensive so is expensive.
For clay chips, the colored edge spots are made by cutting out holes in the solid-colored blank where the spots will go, then cutting out spots from a different colored blank chip, then putting the spots from the second chip into the holes in the first chip,
and then putting the whole chip into a compression mold and pressing the chip under high heat and pressure. That fuses the spots and blank together.
The process looks something like this:
View attachment 664909
For injection-molded chips, the molds are cleverly designed so that the chip can be molded in multiple stages. Each stage uses a single color of plastic. First, a metal slug is placed in the first mold, and a layer of plastic is molded around that using the spot color; that stage has a thin layer through most of the body but is thick where the spots go. Then the chip is placed in a second mold, and another layer is molded around it, this time using the body color, producing the final chip.
Some plastic chips use three or even four colors of plastic, and their molds are even more complex.
This is called "two-shot" or "multi-shot" injection molding.
This page has a nice overview, with this simple video:
Here's a video of an actual multi-shot injection mold in use, and it works somewhat like the molds for poker chips work. First the metal body of a flash drive is inserted into the mold, then a white shell is molded around the metal body, then a green shell is molded around the white, then a blue shell around the green, and then finally the completed part is removed from the mold:
You can see the results for a poker chip in this picture. Furthest inside is a metal slug. The orange spots are molded around that, then the red body is molded around the spots. Finally an adhesive label is stuck onto the finished plastic chip.
View attachment 664929
I hope this answered some of your questions!
