How are 3D images etched into glass and how were blue LEDs created?

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In summary, the LEDs inside the rotating glass block were blue. The pattern was made by etching into the glass. The display was made with a rotating platform and four fixed LEDs. The display is not high-tech and is for souvenirs.
  • #1
Janitor
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Okay, so this is really two questions, one having to do with electrical engineering, and the other having to do with materials processing (a name I just made up).

I was at a museum, and I saw on display a rotating platform that held a slab of clear glass. Inside the glass there was a milky 3D image of a steam locomotive. The locomotive pattern had the look of etched glass, but heretofore I have only seen etching on the surface of glass, and this pattern was most definitely in the interior of the block of glass. There were no seams in the glass. As the glass rotated, the locomotive lit up in four colors: red, yellow, green, and blue. A museum worker lifted the glass up and let me look at the clear platform that it sat on. Under the rotating platform there were four fixed LEDs, shining in the aforesaid four colors.

So the EE question is: when and how did they make blue LEDs? I can remember red and green being common when I was young, and then they came out with yellow (a.k.a. amber), which if I recall somehow combines the red and green technology to put out a mixture of light that looks yellow. But blue LEDs are something new to me.

Second question: how do you etch (if that is even the right term for it) the interior of a chunk of glass?
 
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  • #2
Blue LEDs exist for more than a decade. See here.
About the glass etching I don't know. Is it possible that the locomotive you saw was a holography?
 
  • #3
Make a laser beam come into focus inside the glass block.
 
  • #4
SGT's link says that gallium nitride is the material needed to make the blue LED. Thanks for that link.

Averagesupernova, are you speculating, or have you heard that this is how it is done? If is is some sort of heating effect, what is happening to the heated glass that makes it form opaque spots at the point of focus? Opacity due to surface etching is presumably due to roughening of the glass surface by a strong acid, such that the glass is no longer a nice flat plane. I am not seeing how internal roughening would result from application of heat. Do you have a link on this topic?
 
  • #5
SGT said:
... Is it possible that the locomotive you saw was a holography?

Not if my understanding of holography is correct. The image remained visible to the eye as a white-colored 3D pattern even when viewing the glass under ordinary room lighting.
 
  • #6
Janitor said:
Not if my understanding of holography is correct. The image remained visible to the eye as a white-colored 3D pattern even when viewing the glass under ordinary room lighting.

I think that with red, green and blue laser diodes you could obtain a white holographic image. Of course there must be a focusing system to achieve that.
 
  • #7
SGT said:
I think that with red, green and blue laser diodes you could obtain a white holographic image. Of course there must be a focusing system to achieve that.

I note that these were just four ordinary LEDs with their hemispherical plastic "lenses" pointing straight up, such that at any given time the locomotive might be catching only one or two colors. If you were to stop the rotation of the platform, the front of the locomotive might be green while the rear of the locomotive might be yellow, with the red and blue lights missing the pattern and passing through the block of clear glass without scattering. The base/platform part of the display looked like something you could make at home for no more than $10 in parts. It was not at all what you would call high-tech. The pattern inside the glass, on the other hand, looked like something that a home hobbyist would have no chance of being able to make.
 
  • #8
Averagesupernova was correct about the use of laser. They are used to fracture the glass at the focal point... check http://www.bathsheba.com/crystal/process/
This is being done a lot now for souvenirs.
 

What is the significance of the museum display?

The museum display showcases important artifacts, artworks, or historical items that hold significance and provide a deeper understanding of a particular subject or time period.

What is the purpose of the museum display?

The purpose of the museum display is to educate and inform visitors about a specific topic or theme through a curated collection of objects, documents, or multimedia presentations.

Who decides what is included in the museum display?

A team of experts, including curators, historians, and subject specialists, work together to select and arrange items for the museum display based on their relevance, historical value, and educational potential.

How are items preserved and maintained in a museum display?

Museum staff carefully handle and store items in a controlled environment to prevent damage from light, humidity, and other factors. They also conduct regular inspections and conservation treatments to maintain the integrity of the objects.

How do museum displays contribute to scientific research?

Museum displays provide a platform for scientists to share their findings and discoveries with the public. They also allow researchers to study and analyze artifacts and specimens for further understanding of their significance and historical context.

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