Optical Illusion

[Photobuff]

I've been in copper bolt heaven. Even though most of the survey disks around the rail lines here have been destroyed, the copper bolts in the bridges and culverts have survived nicely. Today I found one with an inscription cut into the stone, identifying it. Naturally I took a picture of it. Here's the interesting thing. Sometimes when I look at it, the lettering looks raised out of the stone. Other times it looks cut like it should. Or, I blink and suddenly it's wrong again. Obviously I should have done something different with the lighting so there'd be no question. Anyway, have a look at NB0866 and tell me what you see!

[+Mr Lost]

I've been in copper bolt heaven. Even though most of the survey disks around the rail lines here have been destroyed, the copper bolts in the bridges and culverts have survived nicely. Today I found one with an inscription cut into the stone, identifying it. Naturally I took a picture of it. Here's the interesting thing. Sometimes when I look at it, the lettering looks raised out of the stone. Other times it looks cut like it should. Or, I blink and suddenly it's wrong again. Obviously I should have done something different with the lighting so there'd be no question. Anyway, have a look at NB0866 and tell me what you see!

The glass is half full.

[mloser]

Actually that is a common optical illusion and has to do with the direction of shadows. Here is Oracle's version of the reason: How to Create an Optical Illusion. I flipped the original picture and put it back with a note at NB0866 so you can see it with the shadows oriented so your brain processes them as expected. The lettering looks indented.

[Bill93]

Interesting illusion. I have trouble getting past the raised look to see it carved in. The lack of obvious shadows elsewhere leaves the mind with few clues to interpret the shading of the groove.

 

That is some beautifully done lettering. They must have hired the guy who made cemetery stones to carve it.

[Photobuff]

mloser- I didn't put in the upside down version, but am glad you did. Even that doesn't always work for me. I printed out the image, and see it as engraved when upside down. If I slowly turn it over, it still looks engraved. If my eye flashes to the dark area and back, it looks raised. Then, if I turn it over slowly, it still looks raised, even upside down. Sometimes I can't see it as engraved no matter what I do! First noticed this effect with a benchmark disk, shot under the same sort of conditions. Just wondered if it happens to others.

[+Klemmer]

Oh, yeah! How did the stone carver get the letters all raised like that? Did he use some stone dust & molded it with epoxy, or what?

 

[i've always thought that when you could get an illusion like that, it was the sign of a good picture!]

[mloser]

After I posted I realized that I didn't just turn it around, I also flipped it horizontally. Fixing the illusion in this image is not as easy as with ones that have clean shadows--the mind has to process other things in the image besides just the letters and shadows.

[Z15]

The lettering was done with a stencil. Looks like they chiseld away some stone and placed some motar they used to set the pin with and stenciled the lettering. I have seen some of the old stencil kits in the past for concrete. stations along highways.

Edited January 25, 2006 by Z15

[mloser]

Well, there is another illusion! The illusion that everything old is hand crafted.

[Photobuff]

I'm not positive about how this was done. At first I thought they might have used the cement trick, but any cement I've ever seen wouldn't have held up this well. IMO, it's probably over 100 years old. The lettering, in spite of my photo, is sharp and crisp, as it would be if cut into the stone. It looks cut into the stone, though the smooth area does also have a cementish look to it. Local cemeteries have lots of lettering like this, cut into stone, and they also have raised lettering- probably an extra cost option. I don't know much about cement- ok, nothing! Are there smooth cements that weather better than the gravel filled stuff I'm used to?

[Z15]

look at how smoothe the surface is at the stencils compared to the rest of the stone. It even appears a different color.

 

Motar is fine sand and portland cement. If mixed correctly I am sure it would have lasted a long time. Could have been some special mixture like they used to set disk in headwalls, buildings etc. Those never fall out.

Edited January 25, 2006 by Z15

[mloser]

Ah! Light bulb. When you said stencil I thought you meant they used it to mark the letters and then carved them in, not stencil in concrete.

 

After looking at it, I think it is definitely carved into stone. There are marks at the perimeter of the lettering that make me think the area was smoothed down with a wide chisel, then the letters were incised into the flattened area. Nothing about the appearance of that surface looks like concrete or any cast material at all.

 

I have seen about 10 of these sets of carved letters and I never even thought they were not just carved into the material. KW1860 is one that is definitely carved into rock, although not as neatly as NB0866. KW0735 is another, and this one also looks like the letters are raised. Just like Photobuff's mark, they are carved INTO the stone face.

[+BuckBrooke]

I've seen this effect in flipping through benchmarks. On a related note, Florida SRD (?on which agency?) has an inset metal disk (as usual), and then also has what looks like the disk, but it looks like part of the concrete surface, with the letters and two boxes for letters coming out of the surface. Almost like they had a stamp that they stamped into the concrete. Although it's above the surface.

 

I can't find the original disk, but here's what looks like the stamped disk: AD2614.

Edited January 25, 2006 by BuckBrooke

[ArtMan]

I have photographed a number of disks where the stamping appears raised. So the same optical illusion that applies in stone/concrete also works in metal.

 

-ArtMan-

[+GeckoGeek]

I don't know why, but I just can't get them to pop out at me at all.

 

But I think there is a couple of factors to the illusion. First is where the shadows are - our brain is used to seeing shadows below, not above because the sun is usually "up".

 

Second, we expect to see indented things as in shadows and "out" things as being highlighted. But if the carved out area is lighter then the surface, that can create confusion when looking at a 2D (photo) of the object.