Oystein, I may be mistaken in my memory. Pgimeno showed us what Ivan was able to pull off a screen shot, which may be all there is. There have been comments by Jones, Ryan and Harrit, but perhaps that's all I've actually seen.
We'll see if Ziggi can help us locate more data
Sunstealer, if you're still around, can you tell me what the TEM data might show us if it were released by the Harrit/Jones/Ryan/Farrer team? Alternatively, Oystein perhaps you can help... ideally something quoting someone like Sunstealer or at least your understanding of what light TEM data can shed on this.
Got no quotes, only my limited understanding.
So far we have seen SEM data from Farrer and Jones - Scanning Electron Microscopy. The specimens for this technique can be thick and bulky - the microscopy "scans" electrons (or, with different dectors, X-rays) that are returned from near the surface of the specimen. Several pathways and methods apply. Electrons hit the surface of the sample, penetrate to some depth even (micrometer scale), get scattered, often excite atoms and cause them to emit secondary electrons, and may leave the probe again at some other angle. That behaviour depends on the density of the material and the atom species the electron encounter. Because the original electron and its secondary electrons and xrays "bounce around" and explore a certain depth, it is difficult to focus on individual pigments; in our chips, you always pick up information from material surrounding the spot of interest.
A TEM (Transmission Electron Microscopes) essentially looks at electrons that have passed through a specimen, which gives us a requirement for sample preparation: Specimens mut be very thin (well under 1 µm). TEM allows for a higher theoretically possible resolution (SEM is limited at best to perhaps nm, TEM goes well under 1 nm) and better focus, but sample preparation may be a more difficult art. The upshot is that an electron focused on a spot of interest passes only through that spot and doesn't pick up information from surrounding material. This allows for better focus.
TEM, like SEM, can be equipped with X-ray detectors to allow for XEDS data (elemental identification), and that is, given competent sample preparation, higher quality then SEM-XEDS. It is better possible to get XEDS data on really just a single pigment, with less or no matrix or neighboring pigments interfering.
TEM (but not SEM) can additionally be equipped for "
Selected area electron diffraction" (SAED), a method where electron waves passing through gaps between atoms form diffraction patterns if the atoms are regularly spaced in a crystal lattice. The diffraction patterns are characteristic for different crystals and thus constitute a method to identify the crystal species. Millette employed this method and identified the hexagonal, Al-Si-rich platelets as crystals of kaolin.
Now, what to expect from Farrer's TEM data? It would depend on his objectives and hence on his sample selection, sample preparation, and the equipment he used in addition to mere electron detection. We know that he has identified trace elements (Sr and Cr as well as Pb), so he apparently used TEM-XEDS. I would expect that he has high-resolution images of the sample areas from which he got the Sr and Cr signals, so we can see if they originate from a pigment, or from an area within the matrix, and whether or not the two elements go together, or are distributed independetly from one another. This would either strengthen or dispel out theory that there are pigments of strontium chromate: TEM can be expected to show those pigments individually (they tend to be larger than the iron oxide pigments, and are typically needle-shaped (acicular), meaning they are several times (for example 10x) longer than thick) and yield XEDS spectra showing mostly O, Cr and Sr peaks.
I have seen nothing that suggests that Farrer used SAED with the TEM. If he did (but, I must stress, I don't think he did), he should no doubt have identified kaolin and hematite as well, and could have been in a position to pinpoint other pigments and fillers as well (strontium chromate in LaClede chips; quarz, zinc chromate, calcium silicates and aluminates, talc in Tnemec; possibly lead chromate in other paints; etc.)