The ‘Escences' of Light: All About Color, Part IV

Peacock feather earrings

Yes, I know that "essences" is spelled with three S's, but that is not what we are featuring today. I want to discuss the subjects of iridescence, pearlescence, opalescence, luminescence, phosphorescence and fluorescence. We touched on these topics when we discussed structural color and observed iridescence in a peacock feather and a butterfly's wings (August 14, 2019 post). Now I want to treat iridescence and its related phenomena in greater detail.

Soap bubble

Iridescence is an optical phenomenon that appears  when certain substances seem to change colors as the viewer changes the angle of observation, or the angle of light changes. You have seen it on the surface of a soap bubble. feathers, insect wings, oil slicks on wet pavement and the insides of some seashells. Often the effect is the result of structural color caused by microstructures in the material that interfere with the direction of light rays. The word iridescent comes from the Greek word iris, which means "rainbow" and the Latin word escent which means "having a tendency toward". (Learn more about the origin of the word in our April 27, 2020 post.)

Oil slick on wet asphalt

The thickness of the layers of the iridescent materials influences the pattern of light interference. Thin films like oil slick or soap bubbles are most likely to produce temporary iridescence. In an oil slick, the different colors indicate different thicknesses in the layers of oil.

Hummingbird photos by J.J.

More permanent effects are caused by many layers of structure like those in a hummingbird's feathers, the scales of a butterfly's wing, or the layers of nacre in an abalone shell. The range of colors in natural iridescence may be narrow, shifting between only 2 or 3 colors, or as wide as the whole visible spectrum. The rainbow colors require quite elaborate arrangements of micro-structure.  A few minerals show this kind of iridescence. One of the most startling places to find the effect is from the iridescent scales on the abdomens of tiny male peacock spiders from Australia. This is easily mistaken as a threat display, but it is really part of an elaborate courtship routine. And he had better do it right or the female will kill and eat him! (You can see his performance on You Tube or BBC).

We can create artificial iridescence with diffraction, which in this case refers to the spreading of light around an obstacle or forcing it through a small opening, creating an interference effect.  We see the affects of this in DVDs, CD's, smart phones with iridescent back panels, and glitter nail polish.

Mother-of-pearl inside shell

Pearlescence is an effect related to iridescence where some or all of the reflected light is white and iridescent effects produce rainbow colors. The term pearlescence is used to describe the situation when a structure within a surface causes light to be reflected back, but some or all of the light that is reflected back is white light. However, pearls can be many colors besides white — pink, blue, green, gold, grey or rainbow-colored. Artificial pearlescence can be made with certain pigments and paints. This effect is largely used in the automobile industry.  Pearlescent paints and finishes can be found in craft paints and nail polishes, as well.

Fresh water pearl jewelry

Natural pearls occur in the soft bodies, or mantles, of mollusks like oysters and some species of freshwater mussels. The pearl is composed of calcium carbonate in response to the presence of an irritating intruder in the shell. Most people believe that the irritant is a grain of sand, but it is far more likely to be a parasite. A sort of allergic reaction by the mollusk causes a pearl sac to close around the intruder.  Tiny crystals are deposited around the sac in layer after layer. This process goes on as long as the mollusk is alive. Perfect pearls are round, but pearls come in many shapes, depending upon the shape of the irritant inside. Irregularly-shaped pearls are called baroque pearls. Cultured pearls are "grown" at pearl farms where small particles are inserted into the mollusks' bodies. In this way the size and shape of the resultant pearl can be controlled.

Opalescence is an optical phenomenon displayed by the gemstone opal. This is due to the layering, spacing, and size of the many crystals of silicon dioxide, in the form of microscopic spheres, and the included water and/or air in their microscopic structures. When the sizing and spacing of the spheres is small, refracted blue-green colors are prevalent, sometimes with flecks of other colors.  This is precious opal. You can see it in the opal set into the head of this silver fish pin. The dark spot in the "eye" is a bit of stone around which the opal formed.

Precious (top) & common white opals

When the sizing and spacing of the molecules is somewhat larger, the colors yellow, orange, and red appear. This kind of gem is called fire opal. When the sizing and spacing is larger still, a milky, hazy sheen of light appears within the stone. This material is called common opal.  Exposure to heat can cause the water in the stone to break down and the fire and glow disappears. The stone is said to 'die'. During the Bubonic Plague, this effect was seen when the wearers fell prey to the extremely high fevers that the disease caused. Because people at that time did not understand diseases very well, the opals were sometimes blamed for the wearers' deaths. It became a forbidden gem and didn't regain its popularity until the 20th Century.

Honduran black opal

Opal can be found as inclusions in many different minerals. It can form in wood which later becomes petrified. It has also been found in fossil shell and bone. It is a fairly soft material, which is often "sandwiched" between a layer of dark stone, to reflect more of its brilliance, and a hard, clear quartz to protect it from wear.  It needs to be protected from heat, and opal rings or bracelets should never be worn while washing dishes.

Phosphorescent pigment before & after 'charging'

Phosphorescence occurs when the phosphorescent material is "charged" by exposure to light — usually ultraviolet light. Then the energy that has built up is stored for a period of time and released slowly.  Some minerals, including some diamonds, are naturally phosphorescent. Oddly, phosphorus, for which the phenomenon was named, is not one of them. These materials can sometimes be activated by body heat or by being vigorously rubbed. When the energy is released immediately after exposure to light, the phenomenon is called fluorescence. The study of phenomena like this led to the discovery of radioactivity in 1896.  There are practical applications, such as fluorescent lights and items like clocks that glow in the dark.

Scorpion fluoresces under UV light

Incandescent steel

Luminescence, sometimes called cold-body radiation, is a spontaneous emission of light from a substance that is not caused by heat.  It can be caused by electrical energy, chemical reaction, sub-atomic motion or stress on a crystal. This distinguishes it from incandescence, which is light being emitted by a substance that is being heated. For example, a fireplace poker left in the fire too long might begin to glow.

Luminescence has some interesting practical uses. Some examples are: lasers, light-emitting diodes (LEDs), dosimeters to detect harmful radiation, luminol to detect the presence of blood at a crime scene, and photoluminescence used in microbial diagnosis.  That last use is playing a part in the current fight against corona virus and other causes of deadly epidemics.

Fireflies (30 second exposure)

Bioluminescence is, to me, the most fascinating ‘escence’ of them all. It is light emitted from living organisms.  One summer night long ago I was riding around on dark rural roads with some college friends. Suddenly we saw an area ahead of us that was glowing and pulsing. We stopped, climbed over a fence, crossed a field and reached a tree-shaded place by a creek. On the ground were hundreds of small bodies flashing yellow, green, and a reddish light, more or less in unison. None of us had ever seen glowworms, but we realized that was what they were. Glowworms are the females of some species of fireflies (which we called "lightning bugs"). Their heads and eyes mature to adulthood, but their bodies remain in the larval state — unable to fly. We knelt down to watch. After a few minutes, we became aware of smaller pulsing lights overhead. The males had arrived. They flew intricate back-and-forth patterns before dropping down to mate with their choices of females. As mating progressed, the females went dark and the males flew away. They may have been an unnamed species, because they rarely flash red and the males are supposed to attract the females — not the other way around.  We walked in awed silence back to the car, aware that we had experienced something rare and wonderful.

Bioluminescent comb jellies

You may have recently seen film of surfers riding glowing waves at night along the California coast. The light was caused by algae in the water, disturbed by the rolling waves. It is a charming sight, but not a welcome one for scientists. The algae use up much of the oxygen in the water. If they stay around very long, this causes harm to the beds of giant kelp in the water, along with all the marine life that lives in their shelter. This can also be harmful to migrating marine animals like whales and dolphins.

Bioluminescent sea creatures

Most bioluminescent animals live in the sea. Exceptions are the fireflies, some earthworms, and a few cave species that use luminescence to attract prey. Click beetles use flashes of light when in flight to attract mates, but they also flock together on the ground and appear to use the lights as a warning signal there. Some fungi are luminous, perhaps to attract animals that will carry some of the fungal spores away with them.  Bacteria may be luminescent. Many organisms produce their own light, but others harbor luminous bacteria in various parts of their bodies.

In the ocean, particularly at great depths, many — perhaps most — animals have some luminous features. As we develop better and better instruments to send back information on sea-floor dwellers, we are seeing some wild and wonderful luminous species. Animals use luminosity for a number of reasons. An obvious one is to identify mates of the correct species and attract them.  A sudden flash of light to confuse or startle a predator comes in handy.  Being able to mimic another animal — particularly one that is poisonous or just tastes bad — is a distinct advantage.

Angler fish (public domain illustration)

A marine animal that spends a lot of time close to the surface, like a firefly squid, may have luminous organs on the underside of its body that break up its outline and allow it to appear to be part of the surface waves. The angler fish dangles a luminous lure above and in front of its huge mouth to collect unwary prey. His stomach stretches so much that he can eat animals that are nearly as big as he is!  Some sea creatures use clouds of luminescent bacteria the same way the octopus uses ink — to provide a "smokescreen" while making a quick getaway. Animals that regularly eat luminous prey usually have opaque black stomachs. After all, it doesn't pay to advertise your last meal to a predator who might make you its next one!!

I hope you have enjoyed our excursion into the ‘escences’.

 This post by Annake's Garden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

That's a Good Question!: Summer 2020 Q & A

Some of Annake's aids

Ordinarily I do seasonal Question and Answer posts, but I haven't kept to that schedule lately. I apologize for that. Having been through a bad flu epidemic when I was in graduate school many years ago, I got worried when the first news of sickness in China appeared in January. I feared that such a large and populous country with so many connections around the word would not be able to confine the epidemic, so we began making long-range plans immediately. When it became evident that the virus was spreading quickly from country to country, we redoubled our efforts. Because I am high-risk, I have been in self-quarantine for about two weeks longer than most of you. I thought that if isolation is difficult for me — when I work from home all the time —- it must be doubly difficult for those who are unused to it. So J.D. and I decided that, along with our planned posts we would create the EXTRAS section of the blog (see the tab on the menu bar above) and fill it with all sorts of things from photo essays to how-to articles and free patterns to teaching units. We have put up a number of these items and plan to do more until mid-summer. Since most of these questions center on topics in our recent post about easing eye and hand problems for older needleworkers, J.D. suggested that we show some of the devices (shown above) that I personally use.

Do you do quickpoint from charts, or on painted canvas?

Click here to download

Either or both, plus other choices as well. I prefer to work from charts because I make my own. By the time I put symbols on graph paper, I have a pretty clear mental picture of what I hope to accomplish. If you are working from a chart in a needlework book or magazine, there are some things to consider. The chart was probably designed for a specific project with well-defined dimensions. If you are doing quickpoint, which is larger than tent stitch and regular cross-stitch, you will need to count squares carefully to figure out just how large your finished project will be. (I add an extra inch all the way around, just in case.)  Most of the charts I put into these posts are meant to be used for a large variety of sizes and colors. but let me give you one that is a little less variable. Because this is a specific butterfly rather than a generalized one, the colors need to be followed closely. You will still need to count squares as described above for the figure to work on the background you have selected.

If you are working on a painted canvas, start in a corner and work a 10-stitch square of the stitch you plan to use  (be ready to take the stitches out if you need to) to see if you will be able to put in the smaller details of the design. 
I buy painted canvases when I can get a bargain, but I paint out the design and replace it with one of my own, either painted on the canvas or outlined on it. You need to examine the canvas carefully because some, especially ones made for kits,  are just starched cotton and don't hold up well.

Monk's cloth

If you are used to working on even-weave fabric like Aida, you can use several easier alternatives. One is monks' cloth, which has easy-on-the-eyes squares, but it requires a lot of preparation. It needs to be pre-shrunk. Then you need to bind the edges or at least put 2 rows of machine stitching around the edges. When I do use it, I back it with non-woven interfacing, which I work through, and use it for something that doesn't get a lot of wear. On the other hand, if you can find a good quality decorator burlap, you can use it just like Aida and get some lovely surface effects with crewel, tapestry, or novelty yarns.

What is wrong with using printed gingham?

Printed vs. woven gingham

I can show you with the two examples in the picture. The fabric on the left is printed gingham.  It is folded so that both the top surface and the bottom one are showing.  Notice how the design doesn't look the same on the wrong side?  There is no guarantee the cloth was printed so that each square wound up with the same thread count or that your cross-stitches will come out the same size. Now look at the woven gingham on the right. See how the squares are the same on both sides of the fabric? This is true whether you are using baby-check, standard quarter-inch check, or one of the  "jumbo" checks. Your stitches will be the same size and will line up properly both horizontally and vertically. The woven gingham is a little more expensive, but is well worth it.

Love the Bear and the Bee. Does it have a title? And are you going to make any more "Close Encounters" pictures?

The things that fit nicely into my typed scripts don't always fit as nicely when J.D. sets the format for publication. The title was too long for the caption, so he left it off. It is "What Kind of Flower Are You?"  The titles are designed to be said by either one of the pair of animals to the other. I try to do one a year, but — as with everything right now — I am running a bit behind. I am almost ready to do the color cartoon stage of the design. Did you know that the word "cartoon" originally meant the complicated chart for a tapestry weaving? I use the term for the stage when I make a full-sized color rendering to trace permanently on my canvas. I may also graph some of the finer details. Since you know how the titles are chosen, I will give you a hint about the two animals — one a mammal and the other not — coming up next.  The title is "Want to Race?"

You mentioned  'Window Wonders' when you were showing tracing a pattern against a sunny window. What are they and what do you do with them?

Some materials for making Window Wonders

They aren't a form of needlework, but they are pretty and fun to do. I make them for craft shows, usually in three graduated parts, featuring a hummingbird, a butterfly, and a flower, but I have done colorful frogs, dragonflies, small tropical fish, and more. I draw my own pictures, but it is easy to trace them from photographs and drawings. You will need an embroidery hoop (wooden or plastic) with a screw adjustment for each individual picture. I usually make a set of three with a 3-inch, a 4-inch, and a 5-inch hoop, but that varies. I use both circular and oval hoops. You can paint the wooden ones if you like and the plastic ones come in colors. You will need permanent markers in a variety of colors. You will need a transparent or translucent fabric that is stiff when you stretch it across the hoop.  Sheer organdy is ideal.  You will also need a small, sharp pair of embroidery or manicure scissors.

Cut a square of the sheer fabric about an inch larger all around than your drawing.  Center the square over the design and trace the design with permanent markers. (Practice on a scrap first.) When the picture is dry, stretch it over the bottom of the hoop and push the top of the hoop down firmly. Pull the fabric until it is as firm as you can make it.  Turn the hoop over and carefully cut away all excess cloth. Fasten the hoops together as J.D. has shown you here.  I hang the 'wonders' surface-side-out in a sunny window. The design can be seen from outdoors and indoors. If you have a light-colored wall across from the window, you may get still another image on it.  Some people hang the item on screened-in porches or sheltered patios. I showed some outdoors in a 40-mph wind once and all survived beautifully. This is a craft that can be taught to children in elementary school. (For more on 'Window Wonders', see the article in our Extras section.)

You mentioned a kind of pattern-making that you didn't discuss because you said it would probably be hard to get the materials for it right now. My mother-in-law has a lot of materials that she lets me use, so she might have what I need. Would you tell me about that technique?

I'll be glad to — and show you as well. Also, I am so glad that you have a good relationship with your mother-in-law. I had one of the best in the world and I miss her greatly. Cherish that relationship. (And I'll bet she will be a wonderful grandma, too.)

I am going to teach you to make a simple hot-iron transfer. You will need the following materials:
    an ironing board
    an iron, preferably a steam/dry iron
    fabric to transfer the design to (cotton is best for beginners)
    a simple design
    a sheet of tracing paper larger than your design
    a transfer pencil (this is the tough one!)
    a pencil sharpener
    straight pins
    scissors

Click here to download

I do a lot of children's patterns, so I am going to give you a simple one. Or you may substitute a design of your own. Mine faces forward, so you don't have to worry about design reversal. If your design is facing to one side, it will be reversed in the finished pattern. If you are going to put words or names in the design, you will need to reverse them before they are added to the design or leave them out of the design and chart them separately.

Draw or trace your design on the tracing paper with a hot-iron transfer pencil.
These red pencils are made by several companies. I use Aunt Martha's™ (2 to a package for around $3.00.) Each pencil will make many transfers.  Keep the pencil point sharp and go over the lines firmly until they look dark. Set the transfer aside.

Finished blackwork owl - no red marks

Cut you fabric at least an inch larger all around than your paper pattern. Set your iron for the proper temperature for your fabric. Press your fabric. Fold it in half lengthwise and press a strong crease along the fold. Refold it in half crosswise and press another pleat. these should meet in the center of the fabric. At this point i like to stitch a row of bright-colored basting stitches down each pleat that I will pull out once the transfer to the fabric is complete. Stretch the fabric flat. Place the transfer penciled side down on the fabric and lift the center of the transfer up with the center of the fabric. Pin the pattern to the fabric all the way around. Set the iron no higher than cotton and put it on dry (no steam). Press the pattern in to the fabric, pressing hard and go back and forth several times, but don't scorch the paper. It takes at least 5 seconds of hard pressure on each line to get a good transfer. Unpin one corner and lift it carefully. Peek under it to see if your lines have been transferred. If not, re-pin it in the same place iron over it until they do. Turn off the iron and unpin the pattern from the fabric.  I gently pull the basting threads out of the fabric at this point. Work the pattern in any needlework style you choose. The red lines will wash out of the fabric with warm water and a good detergent (I like Dawn® dish detergent) when your project is finished.

I hope these clarifications have answered your questions. Keep creating!

Annake's 24" monitor & soundbar - more help for aging senses

 This post by Annake's Garden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.