Laser engraving mirror

[James Aldrich]

I was wondering if anyone has ever laser engraved mirror from the front? I ran across a website that was offering laser engraved mirror. They state that the mirror is etched from the front Not the back. I have been told by some you can safely etch mirror from the front, and by others that you can not. I was just wondering if anyone has ever tried this?
I have been laser etching the mirror from the back. I also sand etch mirror from the front. I like the look of the mirror when it is etched from the front, and would like to laser from the front, but I dont want to cause any harm to the laser.

Thank you
Jim

[Kevin Huffman]

Yes, you can engrave the front of a mirror if you are the company who make the piece of glass into a mirror. The only thing the seperates a mirror from a piece of glass is the mirrored backing.
If you engrave the glass first then spray on the mirrored backing, you have don't any chance of it causing damage to the machine or you.
So yes but you have to do the engraving before it becomes reflective or a mirror.

[Joe Pelonio]

Yes, you can engrave the front of a mirror if you are the company who make the piece of glass into a mirror. The only thing the seperates a mirror from a piece of glass is the mirrored backing.
If you engrave the glass first then spray on the mirrored backing, you have don't any chance of it causing damage to the machine or you.
So yes but you have to do the engraving before it becomes reflective or a mirror.

Yes, but on the other hand if you try to engrave the front of a mirror, glass or acrylic, that's already a mirror, you'll get a nice random etching on the inside of your glass door when the beam reflects off of the mirror.

Added: This place sells the chemicals to make your own mirror, it's not cheap though.
http://www.peacocklabs.com/products.htm#silveringsol

[Dave Jones]

How about if you use a paper mask on the surface?

[Joe Pelonio]

How about if you use a paper mask on the surface?

The problem is that the reflective surface is at the bottom and protected by the clear surface. I have no idea whether the fact that the beam hits the paper first and then the glass would allow the etch to stop the reflection from coming back as it goes along. If you test it use really low power and be ready to stop it.

[James Aldrich]

Thank you all for the information. Etching mirror from the back and then paint filling does retain finer detail than etching from the front. But some images look real nice with the reflection you get from etching the front. I did laser a sample of mirror from the front, and it turned out fine. Again, thanks to all for the information.

Jim

[Lee DeRaud]

If the edges aren't an issue, you can just engrave on a piece of thin picture-frame glass and "laminate" it to the front of the mirror.

[lee maisel]

I do it all the time. You have to remember that on a CO2 laser, it does not penetrate the surface at all to "bounce off" the reflective silvered part of the mirror. A CO2 laser only vaporizes the surface material. (wood burns, so it's a slightly different story) But as far as glass ad acrylic goes, you are not even getting anywhere near the silver.

Even if you did, the beam is tightly focused to the surface of the material, that means that when it got to the silver (if it did) it would be out of focus, and if it reflected back to the cover of the machine, it would be WAY out of focus, and have no effect.

Remember, the internal mirrors on a laser are not silvered on the back, they are coated on the surface for this reason.

[Rodne Gold]

Actually the reason you can do SOME mirrors from the front is cos as the laser hits the glass it fractures it cos of trapped impurities thus the beam itself is refracted by the fracture and is no longer a coherent spot or has anywhere near the power density it should have if it is reflected.
If you had a mirror that used purer glass or optical glass , like a lens , you would get a back reflection with some potential to do harm
If you use a paper mask , you should be safe or safer.
However IMHO mirrors that are front engraved look awful as there is a double image , the front image and the reflected image and laser engraving on glass is marginal at best - its never as nice as sandblasting - so stick to back engraving (which can also be paint filled easily)

[Dave Johnson29]

If you were concerned about reflection then just angle the mirror slightly. Sit one end on a 1/4" stick and adjust focus for the mean.

However there are several factors that have already been pointed out. The IR does not travel well through normal float glass and it is indeed doubtful if it would get to the reflective coating.

If it did get to the reflective coating, the beam is no longer collimated and cannot be recollimated (such a word??) and again as pointed out it would diverge Exponentially as it is now just a normal reflection. Not to mention it has to travel through that float glass again, if there is any energy left.

Just my experince experimenting with lasers for probably 8 years and I am happy to be corrected by scientific fact.

You can test this with a piece of clear glass placed on a piece of soft wood. Laser the glass and see if it burns the wood. I just thought of that and will give it a try today and post results.

James, care to post a pic to allay the fears of others?

[Dave Johnson29]

OK, I did not have any float glass so I sacrificed a beer glass. I hope you people appreciate that!

First pic is after TWO burns at acrylic cutting settings and 20% speed.

Second pic is the paper pulled out and not a mark!

I rest my case. I will get some float scrap at the glass place today but I do not expect any change in the issue. Float glass has about 87% or better IR absorption.