{"id":40213,"date":"2019-12-03T07:45:21","date_gmt":"2019-12-03T07:45:21","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40213"},"modified":"2020-01-06T13:27:04","modified_gmt":"2020-01-06T13:27:04","slug":"lighting-or-material","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40213","title":{"rendered":"Materials &#038; layers"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">Visual material depth<\/h3>\n\n\n\n<p>Explain why wet stones have more vivid colors: water makes light take  longer paths, more absorption. Same reason why wet fabrics or papers are darker, but also slightly  more saturated. <\/p>\n\n\n\n<p>What makes different coatings appear more or less thick? More or less viscous? <\/p>\n\n\n\n<p>A bumpy glossy base will appear deep under a smooth coating, while a bumpy coating might appear less separated from the smooth base. <\/p>\n\n\n\n<p>A metallic base might also be more easily visually separated from a coating. A single layered scratched metallic surface might convey illusions of depth through anisotropy.<\/p>\n\n\n\n<p>The difference in curvature among layers might be more important than the simple difference in height; but the order of layers seems to matter as well. The static and dynamic cases should be distinguished.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The oily bag effect<\/h3>\n\n\n\n<p>I could have called this post &#8220;the wet t-shirt effect&#8221;, but it would  have been more delicate to illustrate the ideas without diverting attention. Consider an object inside a bag, with a liquid layer inbetween the object and the bag; like a leaking olive oil bottle in a plastic bag, or  a greasy croissant in a paper bag. <br> <br>First the transparency of the bag is often affected by the liquid layer,  for two reasons: the liquid may infiltrate the bag material, and it may  cover it as an additional layer. Infiltration usually leads to a darker appearance in reflection, but when looking through the bag in transmission, it increases its transparency. <br>The same phenomenon is actually at work: with the liquid inside, light  tends to be scattered more forward, hence it gets more easily on the  other side, and much less light turns around and get out to participate  in the reflection. The additional layer of liquid on the bag also affects its appearance:  the most obvious effects is that it gets more shiny because of the  liquid\/air interface. <br>But the liquid\/bag interface is also behaving in a way different than  the (dry) air\/bag interface: in particular, light more easily get through this interface, as if the bag were, once again, more transparent. <br>So the two effects combined explain why a wet bag (or t-shirt if you  wish) lets more light get through it; hence the object behinds it might  become more easily visible. But what happens when the object actually gets in contact with the bag?  It suddenly appears much more visible, in some cases nearly as if the bag was not there! <br>I&#8217;d suggest that a liquid layer then forms between the object and the  bag, making it much easier for light to go from the air, to the liquid,  to the bad, to the liquid and finally to the object. Without this liquid layer, the air in-between adds two aditional  interfaces (liquid\/air and air\/object), which tend to scatter light in  other directions. [really? develop&#8230;]<br>[Connect to Veritasium video showing air pockets under water!] <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Tinkering with frost &amp; dew<\/h3>\n\n\n\n<p>Frost and dew form a layer on top of surfaces in fresh or cold mornings  that appear rough and\/or diffuse. I suppose this appearance&nbsp; is due to water droplets distributed more or  less evenly on the surface. What happens when the surface gets rubbed by a curious pedestrian  passing by? <br>In the case of dew, the droplets seem to merge together to form a smooth  water interface. This interface will tend to make the surface slightly darker unless the  surface is oriented to catch a bright light source. <br>In the case of frost, the rubbing will instead tend to add a liquid  layer on top of frost. The result of this additional interface is once again darkening, but  also increased transparency, letting the base material appear below. <br>[Check: need to test these ideas and take photographs!] <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Visual material depth Explain why wet stones have more vivid colors: water makes light take longer paths, more absorption. Same reason why wet fabrics or papers are darker, but also slightly more saturated. What makes different coatings appear more or less thick? More or less viscous? A bumpy glossy base will appear deep under a &#8230; <a title=\"Materials &#038; layers\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40213\" aria-label=\"Read more about Materials &#038; layers\">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":[772],"tags":[],"class_list":["post-40213","post","type-post","status-publish","format-standard","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40213","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=40213"}],"version-history":[{"count":4,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40213\/revisions"}],"predecessor-version":[{"id":40280,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40213\/revisions\/40280"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40213"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40213"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40213"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}