{"id":39431,"date":"2016-08-23T06:59:17","date_gmt":"2016-08-23T06:59:17","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39431"},"modified":"2020-04-20T08:34:39","modified_gmt":"2020-04-20T08:34:39","slug":"colour-and-the-optical-properties-of-materials","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39431","title":{"rendered":"Colour, and the optical properties of materials"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">Colours due to refraction and dispersion<\/h3>\n\n\n\n<p>The electrons, however, can follow the oscillations of a varying electrical field even at visible and ultraviolet frequencies, and it is these which are most important in colour production. This response of the electrons to an applied alternating electric field is called the electronic polarisability. &#8211; p.58<\/p>\n\n\n\n<p>In general, strongly bound electrons, trapped at atomic nuclei or in strong chemical bonds, have a low electronic polarisability and this leads to a low refractive index. <strong>Loosely bound electrons, such as outer electrons on large atoms or lone pair electrons, are highly polarisable and so will yield materials with a larger refractive index.<\/strong> &#8211; p.60<\/p>\n\n\n\n<p><strong>The refractive index of porous materials depends upon the pore shape and distribution, as well as the phase that fills the pore<\/strong>. The polarisation and wavelength of the light are also important variables. To a first approximation, the refractive index of the whole, nt, can be assessed as that of a simple mixture. &#8211; p.62<\/p>\n\n\n\n<p>For many transparent materials a good representation of the variation of refractive index. with wavelength in the visible region is given by Cauchy&#8217;s equation. &#8211; p.65<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The production of colour by reflection<\/h3>\n\n\n\n<p>Interference and colour, as just discussed, should be differentiated from reflectivity. It could be that a certain colour, say red, is produced by interference effects in a film, but whether the colour is readily seen will depend upon the reflectivity of the film for this wavelength. The reflectivity of a thin film in air will be different from that for a thick plate (Equation 3.1), as interference effects from the bottom surface also need to be considered. &#8211; p.101<\/p>\n\n\n\n<p>If the layers are uneven in thickness, or to some extent disordered, a wide variety of wavelengths will be reflected. These will be perceived as white or silver, depending upon the smoothness of the surfaces. This is the reason why a roll of thin plastic film used for food wrap looks silver. <strong>Many insects show silver markings that are similarly made up of thin layers of transparent material of varying spacings.<\/strong> &#8211; p.114<\/p>\n\n\n\n<p>If the film thicknesses are fairly uniform, then a bright colour will be reflected. Such colours are generally referred to as iridescent, meaning that the colour has a metallic appearance and the tone changes with viewing angle. If the layers are uneven in thickness, or to some extent disordered, a wide variety of wavelengths will be reflected. These will be perceived as white or silver, depending upon the smoothness of the surfaces. All of these are referred to as structural colours to differentiate them from colours produced by pigments. &#8211; p.121<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Polarization and crystals<\/h3>\n\n\n\n<p>To summarize, <strong>in all crystals of symmetry lower than cubic<\/strong> the refractive index depends upon the direction of vibration of the light ray. <strong>Any ray not passing down an optic axis is resolved into two rays linearly polarized in two mutually perpendicular directions. <\/strong>\u2013 p.147<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Colours due to scattering<\/h3>\n\n\n\n<p>Tyndall supposed (correctly) that blue light was scattered more strongly than red light, and this blue scattering is still referred to as Tyndall blue. &#8211; p.176<\/p>\n\n\n\n<p>The first important mathematical study of scattering was carried out by Rayleigh, who investigated <strong>scattering by a small insulating<\/strong> (non absorbing) <strong>sphere with a diameter less than one-tenth of the wavelength<\/strong> of the incident light. Scattering by such bodies is referred to as <strong>Rayleigh scattering<\/strong>. &#8211; p.177<\/p>\n\n\n\n<p>The colour of the sky is the result of the wavelength differential inherent in Rayleigh scattering. <strong>Because this is proportional to l\/lambda^4, violet light is scattered far more than red light.<\/strong> However, it is important to remember that all wavelengths are scattered in the Rayleigh pattern, as analysis with a prism will show. This suggests that when we look at the sky in a direction which is not towards the sun, the colour seen should be indigo or violet. In fact, <strong>the sky appears to be blue<\/strong>. This is for two reasons. First, the <strong>solar energy reaching the ground has less intensity in the violet than at longer wavelengths such as yellow <\/strong>and, second, the <strong>sensitivity of the eye to colour peaks in the yellow-green region<\/strong> of the spectrum near to 555 nm. &#8211; p.179<\/p>\n\n\n\n<p>It is found that for small particles the scattering is proportional to 1\/lambda^p, with p = 4, as in Rayleigh theory. As the particle size approaches that of the wavelength of light, p takes values between 4 and 0.2, while p = 0 for the largest particles. In the Rayleigh scattering limit, the forward and backward lobes of scattered irradiance are equal. As the radius of the particle approaches and passes that of the wavelength of light, the forward scattering lobe becomes dominant and the backward scattering lobe becomes negligible. At larger particle sizes, forward scattering remains dominant, but side bands develop representing maxima and minima of scattering at definite angles. The positions of these lobes depend upon the wavelength of the scattered light and so they can be strongly coloured. These coloured bands, referred to as higher-order Tyndall spectra, are dependent upon the particle size and so can be used for particle size determination. For the largest particle radii, wavelength dependence is lost. That is to say, large droplets scatter all wavelengths equally (although the scattering pattern still shows the strong forward-pointing lobe), which is the reason why fogs are white to the eye. [&#8230;] With large particles, white light becomes reflected (rather than scattered as discussed here) evenly in all directions. This is the situation that holds in fogs and mists composed of fairly coarse droplets. &#8211; p.185<\/p>\n\n\n\n<p>Many paints, plastics and glazes are made opaque by the addition of white pigment. Most frequently this is titanium dioxide (Ti02), but china clay and limestone are also commonly employed. These materials are not, in fact, white, but colourless. They give the appearance of whiteness when in powder form (in air) due to surface reflection and scattering. When mixed within a transparent matrix opacity is mainly the result of scattering. <strong>A similar opacity is found in opal glass, devitrified glass, glass ceramics and porcelain, which contain varying amounts of precipitated crystalline phases in a glassy matrix.<\/strong> Both components are transparent in bulk form and the opacity comes principally from scattering by the inclusions. &#8211; p.188<\/p>\n\n\n\n<p>Multiple scattering, particularly in a forward direction, from randomly distributed closely spaced scattering centres caused the diminution in the measured extinction. &#8211; p.190<\/p>\n\n\n\n<p><strong>For strongly absorbing collections of small particles<\/strong> it is found that, although the amount of light scattered is still proportional to V^2\/lambda^4 (the Rayleigh dependence), the absorption of light is proportional to V\/lambda , where V is the volume of the particles which are interacting with the incident light. Now, <strong>as V becomes smaller, the main interaction with light changes from scattering to absorption.<\/strong> Classical Mie calculations with spherical gold particles reveal how absorption and scattering change with particle diameter. &#8211; p.191<\/p>\n\n\n\n<p>When the dimensions of the metallic particles fall below a diameter of 50 nm or so, absorption dominates the colour effects observed. Although Mie theory documents these changes, it does not explain them and is confined to spherical objects. The precise absorption characteristics of these small particles depend critically on the shape and are not well explained in terms of spheres. &#8211; p.193<\/p>\n\n\n\n<p><strong>The actual colours observed (in both ruby glass and the Lycurgus cup and related artefacts) depend strongly upon the particle composition, size and shape and on the density of particles in the glass.<\/strong> Thus, many subtle variations are to be expected in glass made by artisans using relatively irreproducible techniques. &#8211; p.194<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Colours due to diffraction<\/h3>\n\n\n\n<p>When the scattering object is made up of a more or less ordered arrangement of scattering centres, the scattered waves have a close relationship with each other, defined, in part, by the separation of the scattering centres. Under these circumstances the outgoing waves can interfere constructively or destructively and the phenomenon is called diffraction. When the separation between the scattering objects is less than the wavelength of light, similar effects still occur, but the classical diffraction equations are very restricted in application. The scattering is then often called coherent scattering rather than diffraction, although the two processes are identical. \u2013 p.197<\/p>\n\n\n\n<p>The sine of the angle through which a ray is diffracted is related to its wavelength. This indicates that <strong>each wavelength in white light will be diffracted through a slightly different angle, with red light diffracted through the greatest angle and violet light diffracted through the least<\/strong>. &#8211; p.200<\/p>\n\n\n\n<p>It is important to be aware that these orders are not the same as the weak orders from a single scattering object but are new, intense peaks formed by the periodic grating. &#8211; p.205<\/p>\n\n\n\n<p><strong>When the atom planes are stacked up to form a three-dimensional grating<\/strong> (i.e. a crystal), there are further limitations to the diffraction. Once again, a strong zero-order diffracted beam only occurs for &#8216;reflection&#8217; , i.e. when the angle of incidence on the stack of planes is equal to the angle of&#8217; reflection&#8217; off the stack of planes, but in addition, only certain specific values of the spacing between the planes give rise to any significant intensity. This means that <strong>a strong diffracted beam only occurs at a few specific angles of incidence<\/strong>. Similar arguments apply to other orders of diffraction. &#8211; p.212<\/p>\n\n\n\n<p><strong>Precious opal shows flashes of colour from within the stone, blazing out brilliantly over small angles as the stone is tilted. <\/strong>[&#8230;] the regions producing the colours are made up of an<strong> ordered packing of spheres of silica<\/strong> (Si02) which are embedded in amorphous silica or a matrix of disordered spheres. &#8211; p.214<\/p>\n\n\n\n<p>Randomly sited copies of a single object will produce a diffraction pattern which is a brighter version of that of the isolated object. Thus, the diffraction pattern of a random collection of circular apertures or rectangles will consist of the same patterns as described above, but with an increased intensity. &#8211; p.225<\/p>\n\n\n\n<p><strong>Diffraction patterns from random droplets or specks<\/strong> can be seen frequently. Because of the wavelength sensitivity of the diffraction, the effects give rise to colours. One of the commonest of these phenomena is the <strong>corona around the sun or moon, seen through high, thin clouds<\/strong>. They lie close to the disc of the object and are much narrower than the halos described earlier. The pattern is the Airy ring (Fraunhofer) liffraction pattern from the collection of randomly distributed droplets. These add together and an observer, in reality, sees fragments of the diffraction patterns from many droplets or specks, each of which contributes to the overall effect.<strong> When the clouds consist of similarly sized droplets or specks, the effect will be strong.<\/strong> At their best, the coronae show multicoloured rings surrounding the central disc of the sun or moon. For a similar reason, a multicoloured ring can sometimes be seen to surround a narrow beam of white light which has passed through a pane of glass covered with a fine powder or with fine drops of moisture. Each particle diffracts as a small circular aperture. &#8211; p.226<\/p>\n\n\n\n<p>This colour arises by diffraction when the pitch of the helices in the cholesteric mesophase (that is, the repeat distance along each helix) is similar to the wavelength oflight. Scattered light can then interfere constructively. &#8211; p.228<\/p>\n\n\n\n<p>These effects have already been anticipated by nature, and <strong>a number of beetles show iridescent colours due to a cholesteric arrangement of layers of fibres<\/strong> in the outer integument of the body. The fibre direction in each layer is slightly different from that on either side and a helical layered structure is built up. If the pitch of the spiral is of similar dimensions to the wavelength of light then they give rise to intense &#8216;metallic&#8217; colours when viewed in white light. &#8211; p.230<\/p>\n\n\n\n<p>The situation described for a random array of specks or droplets applies equally well to random arrays of two- or three-dimensional gratings. A scattering object which is made up of a random collection of two- or three dimensional gratings will give a diffraction pattern which is a brighter version of that of the isolated object. Here, there are two extra variables to consider besides the random spatial position: the relative orientation of the grating fragments (that is, the relative rotation about an axis parallel to the illuminating light beam) and the physical extent of the grating. Both of these modify the diffraction pattern observed. &#8211; p.230<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Colours from atoms and ions<\/h3>\n\n\n\n<p>In both solutions and crystals, six water molecules are arranged so that the oxygen atoms form an octahedral coordination polyhedron around a central cation. &#8211; p.264<\/p>\n\n\n\n<p>The <strong>two most important geometries<\/strong> to consider, especially for oxide pigments and ceramics, are<strong> octahedral and tetrahedral coordination.<\/strong> &#8211; p.266<\/p>\n\n\n\n<p>The colour of a transition metal ion is then supposed to be due to d electrons moving across the relatively small energy gap created by the crystal-field splitting. The magnitude of the crystal-field splitting will depend on the geometry of the surrounding ions and how close they are to the cation.<strong> In a strong crystal field,<\/strong> produced when the surrounding anions are close to the cation, the crystal-field splitting is large. This means that the transition energy will be large and <strong>any absorption peak will be in the violet or ultraviolet region<\/strong> of the spectrum. <strong>In a weak crystal field, <\/strong>produced when the surrounding anions are further away from the cation, the splitting is smaller and<strong> any energy peak will be in the red or infrared. <\/strong>This variation accounts for the fact that any particular transition metal cation may exhibit different colours in different compounds, as for ruby and emerald. &#8211; p.269<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Colours from molecules<\/h3>\n\n\n\n<p>Whereas a gas of atoms emits light at precise wavelengths to give a series of sharp lines, molecules may emit sharp lines and extended bands. <strong>Each band in a molecular spectrum generally has one sharp side and a diffuse, gradually fading side to it. Under high resolution the bands are seen to be made up of closely spaced series of lines. <\/strong>\u2013 p.309<\/p>\n\n\n\n<p>Electronic transitions can then be considered to be analogous to those in atoms, but now the electrons are switched from lower energy molecular orbitals to higher energy molecular orbitals and vice versa. A molecule may also vibrate, and each single electronic energy level is accompanied by one or more sets of energy levels that correspond to vibrational transitions. Finally, rotation gives rise to further energy level increments which are added to the vibrational levels. &#8211; p.310<\/p>\n\n\n\n<p>The theory underlying the electron energy levels of molecules is, in principle, but a little more complex than that of atoms, and the calculations, using molecular orbital theory, can be carried out routinely. However, in practice, the bewildering complexity of many molecules makes the work feasible only for simpler structures. Fortunately, for our purposes, the <strong>colours arising in molecules can be understood by ignoring almost all of the molecular orbitals and focusing attention upon just two.<\/strong> These are the molecular orbital of highest energy that contains electrons and the first molecular orbital above it in energy that is empty of electrons. In a shorthand notation this pair of orbitals is often referred to as <strong>the highest occupied molecular orbital, or HOMO, and the lowest unoccupied molecular orbital, or LUMO.<\/strong> &#8211; p.310<\/p>\n\n\n\n<p>Although the <strong>vibrational and rotational energy-level separation<\/strong> is too small to give rise to colours, these additional increments of energy can significantly <strong>modify the tone of the gross colour due to the electronic HOMO-LUMO transition. <\/strong>&#8211; p.311<\/p>\n\n\n\n<p>An atomic electronic absorption peak is generally a simple narrow bell shape. In contrast to this, the absorption spectrum for a molecule will consist of a series of bands that can be thought of as approximately occupying the envelope of the corresponding electronic transition. &#8211; p.312<\/p>\n\n\n\n<p><strong>The weak absorption of light in the red region of the spectrum of both water and ice is due to a peak in the absorption spectrum at 760 nm in the infrared, the tail of which extends into the visible. <\/strong>There are also weaker peaks at 660 and 605 nm in the orange-red part of the spectrum which contribute to the removal of the red part of the spectrum. It is difficult to assign these peaks to specific overtones and combinatorial tones because of the multiplicity of possible arrangements available. \u00b7 In the case of ordinary water, the atoms are of fixed mass, but in the liquid and solid states the interatomic bonding is altered compared with the gas phase. The change comes about because of hydrogen bonding, which links the molecules together by additional liaisons. <strong>Hydrogen bonding is stronger in solid ice than liquid water and so the<\/strong> <strong>absorption bands in ice are slightly red-shifted compared with those found in the liquid. This alters the colour of ice slightly, compared with water, making it more blue-green. <\/strong>&#8211; p.316<\/p>\n\n\n\n<p>Theoretical calculations show that the presence of <strong>chromophores decreases the energy between the HOMO and the LUMO. The more chromophores there are in a molecule, the greater is the decrease in energy. <\/strong>Thus, in cases where the main absorption band of a parent molecule lies in the ultraviolet, the absorption band of a daughter molecule containing one or more chromophores is moved towards the visible. In suitable cases the result is the transformation of a colourless parent compound into an intensely coloured daughter molecule. &#8211; p.317<\/p>\n\n\n\n<p>The green colours of various leaf species (strawberry tree, cyclamen, rosemary, sage) are produced by chlorophyll, but the appearance of the leaves differs greatly, due to shape and surface coatings. p.321 (Figure 8.7)<\/p>\n\n\n\n<p>The colour of the pigment produced in a flower depends upon R, and R2 and the sugars attached to the molecule. Although the absorption spectra of all of these derivatives are rather similar, slight changes in the absorption maxima make significant changes to the hue perceived by the viewer. &#8211; p.326<\/p>\n\n\n\n<p>When the chlorophyll production ceases in autumn, the carotenoid pigments become visible and leaves turn yellow. This is the normal autumn colour for many trees. Nevertheless, many of the most spectacular of trees show brilliant orange, red and scarlet colours. These are the result of anthocyanin production as the leaf approaches death. These colours are often brief, coming as a prelude to the final colour change when the leaves turn brown. The brown colours are due to tannins that may be naturally present in the leaves, of oaks, for example, or they may be produced by breakdown of other cell components. &#8211; p.332<\/p>\n\n\n\n<p>A charge-transfer transition is one in which a relatively large redistribution of electron density occurs across the molecule. The electron involved in the transfer is excited from a molecular orbital localized mainly in one part of the molecule into a molecular orbital mainly localised in another part. This can occur in several ways. When two or more metal cations are involved the electron redistribution can involve electron transfer from one cation to another, in a cation-to-cation or intervalence charge transfer. Cations can also give or receive electrons from surrounding nonmetal atoms in cation-to-ligand or ligand-to-cation charge-transfer processes. Finally, the electron redistribution might simply involve charge transfer between orbitals that are largely localized on afferent ligands to give a ligand-to-ligand charge transfer. <strong>Generally, charge-transfer colours are intense<\/strong>; those involving transition metal cations, for example, are much more intense than the crystal-field transitions. &#8211; p.340<\/p>\n\n\n\n<p>Many <strong>cation-to-cation<\/strong> <strong>charge-transfer bands<\/strong> lie in the infrared and overlap into the red end of the spectrum, <strong>giving rise to visually perceived dark blue-black colours<\/strong>. &#8211; p.341<\/p>\n\n\n\n<p>Anions tend to be electron rich, while cations tend to be electron poor, so that <strong>anion-to-cation charge transfer<\/strong> is not unexpected and is <strong>responsible for many of the brightest colours shown by inorganic compounds.<\/strong> &#8211; p.345<\/p>\n\n\n\n<p>The common red-brown colour of bricks, flowerpots and many baked-clay artefacts arises from the same source, as do the familiar warm tones of limestone containing Fe3+ ions, much prized in buildings. &#8211; p.346<\/p>\n\n\n\n<p>The colour reflected by ultramarine is thus blue with purple overtones. In naturallazurite and ultramarine the colour depends upon the exact amounts of calcium, sulfur, chlorine and sulfate present and in particular is deepened by increased calcium and sulfur content, which encourages S3 &#8211; formation. &#8211; p.348<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Colours in metals, semi-conductors and insulators<\/h3>\n\n\n\n<p>The main energy landscape in a solid is then the energy band structure. This process can be viewed as an <strong>extension of the ideas that delocalize atomic orbitals into molecular orbitals, but now these orbitals extend throughout the solid rather than just over the molecule.<\/strong> Thus, transitions in an atom, between sharp energy levels, change into transitions between a HOMO and a LUMO in a molecule and then into<strong> transitions between a lower energy valence band and a higher energy conduction band in a solid.<\/strong> &#8211; p.419<\/p>\n\n\n\n<p>If light falls onto an insulator, it will not be absorbed unless the energy of the incident photons is high enough to promote an electron from the valence band to the conduction band. The photon energy at this point is a measure of the optical band gap. <strong>In a flat band model,<\/strong> this is <strong>a single energy and a sharp step in the absorption spectrum<\/strong> would be expected, called the band edge or <strong>the absorption edge. In real solids the band gap is of more complex geometry, and the transition is not so sharp in practice.<\/strong> &#8211; p.420<\/p>\n\n\n\n<p>The concept of an exciton, therefore, spans the range from a strongly bound electron-hole pair on an atom to a weakly bound pair of virtually free particles moving through the band structure of the solid. In all cases, the excitons are revealed by extra absorption peaks in the spectrum of the material. However, these are mostly observed when the sample is at low temperatures, as thermal vibrations smear out the absorption peaks at normal temperatures. &#8211; p.424<\/p>\n\n\n\n<p>In an (inorganic) insulator, the upper conduction energy band is completely empty and the lower energy valence band is completely filled. <strong>As the band gap shrinks,<\/strong> a profound change comes over the colour (and electronic properties) of <strong>the insulator<\/strong>, which gradually <strong>becomes an (inorganic) semiconductor.<\/strong> Intrinsic semiconductors have a similar band picture to insulators except that the separation of the empty and filled energy bands is small. &#8211; p.436<\/p>\n\n\n\n<p>lf the band gap energy falls in the visible, between approximately 1.77 and 3.10 eV, the semiconductor will absorb all photons with energy greater than the band gap energy and not those with a smaller energy. This will cause the material to be strongly coloured. &#8211; p.437<\/p>\n\n\n\n<p>Band gaps of semiconductors can be finely tuned by making solid solutions spanning the composition range between two isostructural parent phases. &#8211; p.440<\/p>\n\n\n\n<p><strong>Metals are defined as materials in which the uppermost energy band is only partly filled. This can be imagined to be the logical outcome of shrinking the band gap of a semiconductor to zero. <\/strong>The key point about a metal is that the higher empty electronic energy levels of a metal are so close to the uppermost filled levels that they form an essentially continuous band of allowed energies. Above the Fermi energy almost all the levels are empty (at absolute zero they are all empty) and so can accept electrons excited from lower energy levels. To a first approximation this means that <strong>all incident radiation can be absorbed, irrespective of its wavelength.<\/strong> Intuitively, this would lead one to expect that <strong>a metal should appear black. However, each excited electron can immediately fall back to the state that it came from at once, emitting exactly the same energy, causing a flat piece of metal to appear reflective. <\/strong>Exactly the same absorption and emission processes lead to <strong>finely powdered metals having a black appearance. This is because the re-emitted (i.e. &#8216;reflected&#8217;) photons are reabsorbed again in nearby grains and ultimately do not emerge at the &#8216;angle of reflection&#8217; and so do not enter the eye. <\/strong>&#8211; p.477<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Colours due to refraction and dispersion The electrons, however, can follow the oscillations of a varying electrical field even at visible and ultraviolet frequencies, and it is these which are most important in colour production. This response of the electrons to an applied alternating electric field is called the electronic polarisability. &#8211; p.58 In general, &#8230; <a title=\"Colour, and the optical properties of materials\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=39431\" aria-label=\"Read more about Colour, and the optical properties of materials\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[621],"tags":[],"class_list":["post-39431","post","type-post","status-publish","format-standard","hentry","category-books"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/39431","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=39431"}],"version-history":[{"count":14,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/39431\/revisions"}],"predecessor-version":[{"id":40372,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/39431\/revisions\/40372"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=39431"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=39431"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=39431"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}