# Physics about Seurat's painting [closed]

The following figure is Georges Seurat's work: A Sunday Afternoon on the Island of La Grande Jatte,created by the technique known as pointillism, in 1884-1886.

This painting consists of closely spaced small dots (around 2mm in diameter) of pure pigment. My question is about how can one find the right position to appreciate the painting for considering the diffraction effect?

• What "diffraction effect" are you hoping to see? – sammy gerbil Feb 18 '17 at 1:47
• I mean we need consider the diffraction effect to enjoy the work perfectly. – Jack Feb 18 '17 at 2:00
• Yes but what "diffraction effect"? How does diffraction happen in this painting, and what visual "effect" does it create which enables us to enjoy the painting perfectly? Perhaps you are asking, how far away from the painting do we have to be so that we cannot distinguish individual "points"? – sammy gerbil Feb 18 '17 at 2:15
• I gave an answer below but now I must improve it. The human eye has a an effective resolution determined by the size of the cells in the retina and the diffraction limit of the eye lens. So in these paintings due to resolution the points come together, if we stand too close we can see the dots. – PhysicsDave Mar 1 '17 at 17:34

You don't see the diffraction effect because you are viewing the painting with normal (full spectrum, incoherent) light, scientists observe diffraction by using monochromatic coherent light. Also you need a slit or similar obstacle.

You won't see any diffraction effects. Nice painting and amazing technique.

I gave an answer above but now I must improve it. The human eye has a an effective resolution determined by the size of the cells in the retina and the diffraction limit of the eye lens. So in these paintings due to resolution the points come together, if we stand too close we can see the dots.

As the answer above says, the painting in your post does not display diffraction effects, but the above opals do. Although there is no human involvement in the creation of these natural, "impressionistic" objects, apart from finding them and polishing them, diffraction effects might possibly be found in stained glass windows.

Diffraction techniques are used in the analysis of the pigments used in paintings, and also in

Diffraction Grating Art

I am discounting CD's, as in my opinion they don't resemble anything normally considered as a painting, unless you like Mark Rothko type abstract works, but again there is no diffraction effect in his paintings either.

Image and Extract From Causes of Color

The play of color seen in opals is attributed to diffraction. Under suitable conditions, water percolates through the earth. Silicates encountered in the soil dissolve into this water to form a silicate-rich solution. When it enters a cavity, the water deposits the silicates as tiny spheres. The layers of precipitated silica spheres form a jelly-like water mass, sometimes producing a diffraction grating when the spheres are even in size and well ordered. The diffraction grating arrangement creates a play of rainbow sparkling light from within the stone.

The play of color is due entirely to the uniformity of tiny spheres, each in the order of a tenth of a micron in diameter. If the spheres are random in shape and arrangement, common opal is formed. If they are uniform in size and shape, they will diffract light and the play of color is evident. The colors caused by the regularly packed spheres making up the internal structure in an opal depend on the size of the spheres and the voids between them. If you move the stone, light hits the spheres from different angles and you perceive a change in color.

The size of the spheres has a bearing on the color produced. Smaller spheres (less than about 150 nm) bring out blues and violets from one end of the spectrum. Larger spheres (no larger than about 350 nm) produce oranges and reds. These spheres are so small that this size difference translates to a difference between roughly 3 million "larger" spheres and 6.5 million "smaller" spheres lined up within the space of a millimeter. The more uniform the size of the spheres, the more intense, brilliant, and defined the color will be.