Anomalous Colours Research Articles

Anomalous colours, not interference colours or ‘apple-green birefringence’, in Congo red-stained amyloid

Anomalous colours, not interference colours or ‘apple-green birefringence’, in Congo red-stained amyloid

Systematic review of accuracy of reporting of Congo red-stained amyloid in 2010–2020 compared with earlier

Background Almost always, Congo red-stained amyloid between polariser and analyser is said to show “green birefringence” or “apple-green birefringence”. In 2010, we found that not all published images showed green, and not all that did showed only green. This systematic review of more recent papers was to find if there had been any improvement in the accuracy of reporting. Materials and Methods MEDLINE was searched on 15 March 2021 for papers published between 2010 and 2020 inclusive mentioning amyloid and Congo red. These were examined for descriptions of colours, which were compared with images. Papers were searched for mentions of anomalous colours, errors in physical optics, and misquotation of references about polarisation. Results In 374 papers, there were 444 descriptions of colours, with 511 images in 257 papers. The commonest descriptions were apple-green, 249/444 (56%), and green, 105/444 (24%). The description agreed with colours seen in 116/511 images (23%) (previously 64/191, 34%). Green was seen in 342/511 images (67%) (previously 159/191, 83%), but not in 169/511 (33%), although each image was reported to show green. Green alone was seen in 103/511 images (20%) (previously 59/191, 31%), and was combined with at least one other colour in 239/511 (47%). Ten papers included the term anomalous. Eight papers incorrectly said that there was green dichroism, three incorrectly used the term green metachromasia, and two incorrectly mentioned green fluorescence. Twenty-seven papers misquoted references. Conclusions There is widespread and increasing inaccuracy of reporting of colours seen in Congo red-stained amyloid. People persist in saying “green birefringence” or “apple-green birefringence”, even when no green is seen, or there are also other colours. Few appear to appreciate that the other colours are genuine, respectable, and helpful, the physical optical principles that explain the colours are now understood, and the best expression to use is anomalous colours. KEY MESSAGE “Green birefringence” and “apple-green birefringence” are inappropriate terms to describe the findings in amyloid stained with Congo red and examined between crossed polariser and analyser, because green is not always seen, and even when it is, other colours are commonly seen as well. The proportions of colour images showing any green and green alone, and the proportion of descriptions that agreed with illustrated colours, significantly decreased in 2010–2020 compared with earlier. The most appropriate and scientific description of the findings is anomalous colours.

Occurrence of silesiaite, a new calcium–iron–tin sorosilicate in the calcic skarn of El Valle-Boinás, Asturias, Spain

Abstract. Silesiaite (Ca2Fe+3Sn(Si2O7)(Si2O6OH)), the Fe3+ analogue of kristiansenite (Ca2ScSn(Si2O7)(Si2O6OH)), has been found in the calcic Cu–Au skarn of El Valle-Boinás, in the north of Spain, which is the second occurrence of this mineral in the world. The study under optical microscopy shows crystals with a distinct pleochroism, from uncoloured to yellowish, high relief and imperfect cleavage under plain polarized light. Under polarized and analysed light, the mineral shows anomalous colours of interference and hourglass and sector optical zoning. Backscattered electron images reveal compositional zoning mimicking optical zoning with light grey (Sn-rich) and dark grey (Fe-rich) zones. The electron microprobe analyses showed that Fe-rich zones are also the richest in Al and Ti, whereas the Sn-rich zones are richest in Mn. The Fe+3 and Fe+2 proportions calculated by stoichiometry suggest a couple substitution such as 2(Fe,Al)+3⇔(Sn,Ti)+4+(Fe,Mn,Mg)+2. According to this, the formula of the silesiaite can be written as Ca2Fe1-2x+3Fex+2SnxSnSi2O7Si2O6OH, where x is between 0 and 0.4.

Origins of a pervasive, erroneous idea: The "green birefringence" of Congo red-stained amyloid.

Congo red was discovered to stain amyloid by accident in 1922, and Congo red-stained amyloid was shown to be birefringent on polarization microscopy in 1927. Colours, namely green and yellow, were reported under these conditions in 1945, although these are only two of various anomalous colours that may be seen, depending on the optical set-up. In 1953 there began a dogmatic insistence that in Congo red-stained amyloid between crossed polarizer and analyser green alone should be seen, and the finding of any other colour was a mistake. The idea that green, and only green, is essential for the diagnosis of amyloid has persisted almost universally, and virtually all mentions of Congo red-stained amyloid say that it just shows "green birefringence" or "apple-green birefringence." This idea is wrong and is contrary to everyday experience, because green is seldom seen on its own under these conditions of microscopy, and often, there is no green at all. How observers maintain this unscientific position is explained by a study of its historical origins. Most of the early literature was in German or French and was usually quoted in English at second hand, which meant that misquotations, misattributions and misunderstandings were common. Few workers reported their findings accurately, hardly any attempted to explain them, and until 2008, none gave a completely satisfactory account of the physical optics. The history of Congo red-stained amyloid is an instructive example of how an erroneous belief can become widely established even when it is contradicted by simple experience.

The Discovery of Quasi-stellar Objects behind M31 and M33

Abstract We report the discovery of 11 newly found quasars behind the stellar disks of the spiral galaxies M31 and M33 in the fields covered by the Local Group Galaxy Survey. Their redshifts range from 0.37 to 2.15. Most are X-ray, ultraviolet, and infrared sources. We also report the discovery of five normal background galaxies. Most of these objects were observed owing to their anomalous colors, as part of a program (reported elsewhere) to confirm spectroscopically candidate red supergiant plus B-star binaries; others were discovered as part of our identification of early-type massive stars based upon their optical colors. There are 15 previously known quasars in the same fields, for a grand total of 26, 15 behind M31 and 11 behind M33. Of these, only eight were discovered as part of surveys for quasars; the rest were found accidentally. The quasars are well distributed in the M31 and M33 fields, except for the inner regions, and have the potential for being good probes of the interstellar medium in these stellar disks, as well as serving as zero-point calibrators for Gaia parallaxes.

Exploring the functional nature of synaesthetic colour: Dissociations from colour perception and imagery

Individuals with grapheme-colour synaesthesia experience anomalous colours when reading achromatic text. These unusual experiences have been said to resemble ‘normal’ colour perception or colour imagery, but studying the nature of synaesthesia remains difficult. In the present study, we report novel evidence that synaesthetic colour impacts conscious vision in a way that is different from both colour perception and imagery. Presenting ‘normal’ colour prior to binocular rivalry induces a location-dependent suppressive bias reflecting local habituation. By contrast, a grapheme that evokes synaesthetic colour induces a facilitatory bias reflecting priming that is not constrained to the inducing grapheme’s location. This priming does not occur in non-synaesthetes and does not result from response bias. It is sensitive to diversion of visual attention away from the grapheme, but resistant to sensory perturbation, reflecting a reliance on cognitive rather than sensory mechanisms. Whereas colour imagery in non-synaesthetes causes local priming that relies on the locus of imagined colour, imagery in synaesthetes caused global priming not dependent on the locus of imagery. These data suggest a unique psychophysical profile of high-level colour processing in synaesthetes. Our novel findings and method will be critical to testing theories of synaesthesia and visual awareness.

Discrepancies between descriptions and illustrations of colours in Congo red-stained amyloid, and explanation of discrepant colours

Congo red-stained sections of amyloid may show various colours between crossed polariser and analyser. The aims were to see how papers described the colours, to compare descriptions with illustrations, and to explain the colours. In 160 papers on Congo red-stained amyloid, the commonest descriptions were ‘green birefringence’ and ‘apple-green birefringence’. In 191 figures in 82 papers, 59 (31%) showed a pure green colour, 62 (32%) showed green and yellow or blue and yellow, 38 (20%) showed green and a colour other than yellow, mostly red, and 32 (17%) showed other colours. Discrepancies between colours reported and illustrated were noted in 127 figures (66%). Most (77) were between green alone in descriptions and green and another colour in figures, and 30 were between green in descriptions and no green at all in figures. Pure green can be seen in ideal conditions, but more often there are green and yellow, explained by strain birefringence, and green and red or other combinations, explained by uncrossing of polariser and analyser. These other anomalous colours are just as characteristic of amyloid as the pure green colour. Many papers on Congo red-stained amyloid appear to describe what is expected theoretically rather than what is actually seen.

THE DETERMINATION OF REDDENING FROM INTRINSICVRCOLORS OF RR LYRAE STARS

New R-band observations of 21 local field RR Lyrae variable stars are used to explore the reliability of minimum light (V-R) colors as a tool for measuring interstellar reddening. For each star, R-band intensity mean magnitudes and light amplitudes are presented. Corresponding V-band light curves from the literature are supplemented with the new photometry, and (V-R) colors at minimum light are determined for a subset of these stars as well as for other stars in the literature. Two different definitions of minimum light color are examined, one which uses a Fourier decomposition to the V and R light curves to find (V-R) at minimum V-band light, (V-R)_{min}^F, and the other which uses the average color between the phase interval 0.5-0.8, (V-R)_{min}^{\phi(0.5-0.8)}. From 31 stars with a wide range of metallicities and pulsation periods, the mean dereddened RR Lyrae color at minimum light is (V-R)_{min,0}^F = 0.28 pm 0.02 mag and (V-R)_{min,0}^{\phi(0.5-0.8)} = 0.27 pm 0.02 mag. As was found by Guldenschuh et al. (2005) using (V-I) colors, any dependence of the star's minimum light color on metallicity or pulsation amplitude is too weak to be formally detected. We find that the intrinsic (V-R) of Galactic bulge RR Lyrae stars are similar to those found by their local counterparts and hence that Bulge RR0 Lyrae stars do not have anomalous colors as compared to the local RR Lyrae stars.

PLANETARY NEBULAE DETECTED IN THESPITZER SPACE TELESCOPEGLIMPSE II LEGACY SURVEY

We report the result of a search for the infrared counterparts of 37 planetary nebulae (PNs) and PN candidates in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire II (GLIMPSE II) survey. The photometry and images of these PNs at 3.6, 4.5, 5.8, 8.0, and 24mum, taken through the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS), are presented. Most of these nebulae are very red and compact in the IRAC bands, and are found to be bright and extended in the 24mum band. The infrared morphology of these objects are compared with Ha images of the Macquarie-AAO-Strasbourg (MASH) and MASH II PNs. The implications for morphological difference in different wavelengths are discussed. The IRAC data allow us to differentiate between PNs and HII regions and be able to reject non-PNs from the optical catalogue (e.g., PNG 352.1-00.0). Spectral energy distributions (SEDs) are constructed by combing the IRAC and MIPS data with existing near-, mid-, and far-IR photometry measurements. The anomalous colors of some objects allow us to infer the presence of aromatic emission bands. These multi-wavelength data provide useful insights into the nature of different nebular components contributing to the infrared emission of PNs.

Physical basis of colors seen in Congo red-stained amyloid in polarized light

Amyloid stained by Congo red is traditionally said to show apple-green birefringence in polarized light, although in practice various colors may be seen between accurately crossed polarizing filters, called polarizer and analyzer. Other colors are seen as the polarizer and analyzer are uncrossed and sometimes when the slide is rotated. Previously, there has been no satisfactory explanation of these properties. Birefringence means that a material has two refractive indices, depending on its orientation in polarized light. Birefringence can change linearly polarized light to elliptically polarized, which allows light to pass a crossed analyzer. The birefringence of orientated Congo red varied with wavelength and was maximal near its absorption peak, changing from negative (slow axis of transmission perpendicular to smears or amyloid fibrils) on the shortwave side of the peak to positive (slow axis parallel) on the longwave side. This was explained by a property of any light-absorbing substance called anomalous dispersion of the refractive index around an absorption peak. Negative birefringence gave transmission of blue, positive gave yellow, and the mixture was perceived as green. This explains how green occurs in ideal conditions. Additional or strain birefringence in the optical system, such as in glass slides, partly or completely eliminated blue or yellow, giving yellow/green or yellow, and blue/green or blue, which are commonly seen in practice and in illustrations. With uncrossing of polarizer or analyzer, birefringent effects declined and dichroic effects appeared, giving progressive changes from green to red as the plane of polarization approached the absorbing axis and from green to colorless in the opposite way. This asymmetry of effects is useful to pathologists as a confirmation of amyloid. Rather than showing ‘apple-green birefringence in polarized light' as often reported, Congo red-stained amyloid, when examined between crossed polarizer and analyzer, should more accurately be said to show anomalous colors.

The Cosmic Evolution Survey (COSMOS): The Morphological Content and Environmental Dependence of the Galaxy Color‐Magnitude Relation at z ∼ 0.7

We study the environmental dependence and the morphological composition of the galaxy color-magnitude diagram at z ~ 0.7, using a pilot subsample of COSMOS. The sample includes ~2000 galaxies with I_(AB) < 24 and photometric redshift within 0.61 < z < 0.85, covering an area of 270 arcmin^2. Galaxy morphologies are estimated via a nonparametric automatic technique. The (V - z') versus z' color-magnitude diagram shows a clear red dominated by early-type galaxies and a remarkably well-defined sequence described by late-type objects. While the percentage of objects populating the two sequences is a function of environment, also following a clear morphology/color-density relation at this redshift, we establish that their normalization and slope are independent of local density. We identify and study a number of objects with anomalous colors, given their morphology, polluting the two sequences. Red late-type galaxies are found to be mostly highly inclined or edge-on spiral galaxies for which colors are dominated by internal reddening by dust. In a sample of color-selected red galaxies, these would represent 33% contamination with respect to truly passive spheroidals. Conversely, the population of blue early-type galaxies is composed of objects of moderate luminosity and mass, concurring to only ~5% of the mass in spheroidal galaxies. The majority of them (~70%) occupy a position in the μ_B-r_(50) plane not consistent with their being precursors of current-epoch elliptical galaxies. Their fraction with respect to the whole galaxy population does not depend on the environment, at variance with the general early-type class. In a color-mass diagram, color sequences are even better defined, with red galaxies covering in general a wider range of masses at nearly constant color, and blue galaxies showing a more pronounced dependence of color on mass. While the red is adequately reproduced by models of passive evolution, the blue is better interpreted as a specific star formation sequence. The substantial invariance of its slope and normalization with respect to local density suggests that the overall secular star formation is driven more by galaxy mass than by environment.

A Near‐Infrared Search for Counterparts to Three Pulsars in Young Supernova Remnants

We present moderately deep JHKs-band searches for near-infrared counterparts to three energetic pulsars in young supernova remnants: PSR B1509-58, PSR J1811-1925, and PSR J1930+1852. We identify a possible counterpart to PSR B1509-58 (which has H 20.6 mag and Ks 19.4 mag, comparable to the flux extrapolated from the X-ray spectrum) with an X-ray-to-infrared flux ratio very similar to that of the Crab pulsar on the basis of its coincidence with the X-ray and radio positions and its anomalous colors, but whether or not we have identified the correct counterpart remains to be confirmed by future observations. For PSR J1811-1925 and PSR J1930+1852 we detect no counterparts, which seems to be consistent with the X-ray-to-infrared flux ratios implied by other young pulsars.

The embedded star clusters in the nebulae vdB-RN 92 and Gy 3–7 in Canis Majoris R1

We employed $J, H$ and $ K_{\rm s}$ photometry from the 2MASS Point Source Catalogue to study the embedded star clusters in the nebulae vdB-RN 92 and Gy 3–7, which are located in the molecular cloud Canis Majoris R1. We employed colour-colour and colour-magnitudes diagrams together with theoretical pre-main sequence isochrones to derive their fundamental parameters. Ages are based on the fraction of stars with anomalous colours, supposedly of types Herbig AeBe and T Tauri. The vdB-RN 92 cluster has an age of 5–7 Myr and the Gy 3–7 cluster ≈ 2 Myr. The average reddening values are A V =4.4 and $ A_V=6.3$, respectively for vdB-RN 92 and Gy 3–7. The distance found for vdB-RN 92 was 1.5 kpc which is, within uncertainties, compatible with previous estimates for the complex. Gy 3–7 also appears to be related to the CMaR1 complex. We conclude that CMaR1 is a very active star-forming site, now with four star clusters in early evolutionary stages.

The embedded star clusters in the nebulae NGC 2327 and BRC 27 in Canis Majoris R1

We employed J;H and Ks photometry from the 2MASS Catalogue to study the embedded star clusters in the nebulae NGC 2327 and BRC 27 locate in the molecular cloud Canis Majoris R1. We made use of colour- colour and colour-magnitudes diagrams of the sample objects in conjunction with those of the Trapezium cluster which was used as a template, together with theoretical isochrones. The fundamental parameters were derived for the clusters. The distances found for NGC 2327 and BRC 27 were 1.2 kpc which are compatible with previous distances for the complex. The estimated ages are based mostly on the number of stars with anomalous colours, supposedly of types Herbig AeBe and T Tauri. Both embedded clusters have ages of1.5 Myr. The results suggest the birth of a physical pair of star clusters in CMaR1.

Detecting High-Redshift Evolved Galaxies as the Hosts of Optically Faint Hard X-Ray Sources

We combine deep Subaru near-infrared images of the massive lensing clusters A2390 and A370 with Keck optical data to map the spectral energy distributions (SEDs) of Chandra X-ray sources lying behind the clusters. The three sources behind A2390 are found to have extremely red colors with SEDs consistent with evolved galaxies at redshifts z > 1.4. One source has extremely anomalous colors, which we interpret as evidence for a type Sa SED at a redshift around 2.5. The photometric redshift of another source has been confirmed at z = 1.467 from near-infrared spectroscopy using the Cooled Infrared Spectrograph and Camera for OHS on Subaru. Mapping of optically faint hard X-ray sources may prove to be an extremely efficient way to locate luminous evolved galaxies at high redshifts.

Clump Giant Distance to the Magellanic Clouds and Anomalous Colors in the Galactic Bulge.

I demonstrate that the two unexpected results in the local universe-(1) anomalous intrinsic (V-I&parr0;0 colors of the clump giants and RR Lyrae stars in the Galactic center, and (2) very short distances to the Magellanic Clouds (LMC, SMC) as inferred from clump giants-are connected with each other. The (V-I&parr0;0 anomaly is partially resolved by using the photometry from phase II of the Optical Gravitational Lensing Experiment (OGLE) rather than phase I. The need for V- or I-magnitude-based change in the bulge (V-I&parr0;0 is one option to explain the remaining color discrepancy. Such a change may originate in a coefficient of selective extinction AV&solm0;E&parl0;V-I&parr0; smaller than typically assumed. Application of the (V-I&parr0;0 correction (independent of its source) doubles the slope of the absolute magnitude-metallicity relation for clump giants, so that MI&parl0;RC&parr0;=-0.23+0.19 [Fe/H]. Consequently, the estimates of the clump distances to the LMC and SMC are affected. Udalski's distance modulus of µLMC=18.18+/-0.06 increases to 18.27+/-0.07. The distance modulus to the SMC increases by 0.12 to µSMC=18.77+/-0.08. I argue that a more comprehensive assessment of the metallicity effect on MI&parl0;RC&parr0; is needed.

Fundamental Parameters of CP Stars

The quest for accurate fundamental parameters (M, R, Teff log g, v sin i) of CP stars has been a lasting problem ever since the nature and origin of these stars has been discussed. The main reason for the difficulty lies in the anomalous colours of these stars, linked with their abundance anomalies which are responsible for complicated blocking and backwarming effects. In the following, we review the Teff determinations proposed so far, and show how the Hipparcos results improve the radius and log g determinations of nearby Ap stars.

Cathodoluminescence Properties of CO2-Bearing and CO2-Free Diamonds from the George Creek K1 Kimberlite Dike

The cathodoluminescence (CL) properties of diamonds from the George Creek Kl kimberlite dike are discussed with reference to their complex growth, mantle residence, and deformation histories. Diamonds shown by infrared (IR) spectrometry to contain submicroscopic, highpressure CO2 inclusions are characterized by anomalous CL colors such as pink, pale violet, orange, and brown, instead of the blue colors typically exhibited by CO2-free diamonds. Complex intergrowth relationships between CO2-bearing and CO2-free diamond-growth generations are recognized from CL photomicrographs of CO2-bearing diamonds. CO2-free diamonds commonly exhibit octahedral growth zonation, and growth-sector zonation was identified in a single diamond of cubo-octahedral morphology. The distribution of platelets that form during prolonged mantle residence time is related to initial nitrogen concentration and thus is influenced strongly by growth zonation. The extreme heterogeneity and complex growth history of the George Creek diamonds...

DELTA-S METALLICITIES OF 35 FIELD RR LYRAE STARS AND THE NATURE OF BB VIRGINIS AND AR HERCULIS

ABSTRACT Preston Delta-S metallicities are derived for 35 type ab field RR Lyrae stars from low resolution (9 A) scans with the Intensified Reticon Scanner (IRS) on the Kitt Peak No. 2 0.9-m telescope. No abundances were previously known for 14 of these stars. The rms error in the Delta-S derived from one of these IRS scans (of good quality) was ±1.6 ( ±0.25 dex in [Fe/H]). The anomalous colors and spectra of the type ab RR Lyrae BB Virginis can be understood if it is a binary_ whose non-variable component is a blue horizontal branch star; in this case the Delta-S of the RR Lyrae component is 9. It is speculated that the unusual colors of AR Herculis may have a similar explanation; techniques for finding further members of this class are considered. The advisability of using the Ca II K-line alone for determining metallicities is briefly discussed.

Single-crystal optical absorption spectra for magnus-type salts of palladium and platinum

Single-crystal optical absorption spectra for magnus-type salts of palladium and platinum