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David Hicken
11-10-2007, 1:24 AM
First, kudos to all of you for making these forums such a valuable tool for those of us just getting into the business. I owe much of what I know to all of you!

We have decided to pursue the direction of etching glass for picture frames. The concerns I have are, once the glass has been etched, there are small shards or fragments of glass which easily come off the etched area. My business partner would rather have the etched side facing the picture, I think we should have the etched side out. My partners concern is people brushing against the etching and getting minor skin irritations. My concern is the small fragments coming lose and ruining the picture, and sometimes irreplaceable picture. Any words of wisdom? Does anyone know if either of these concerns are valid, and what the best practice would be? Thanks in advance.

Darren Null
11-10-2007, 3:08 AM
When you laser glass, the etched image is made up of lots of conical chips of glass that are removed from the surface. Throw your etched glass in with the washing up and that should remove most of the loosened glass chips caused by the etching process. Damage to pictures should then be nonexistant.

Inside or outside...inside you're not going to get any problems with the picture being damaged, but the thickness/quality of the glass may obscure details of your etching. Outside your etching will be clearer, but there will be a rough surface...personal preference.

Rodne Gold
11-10-2007, 5:24 AM
The shard effect is a problem , not cos of the shards , which can be removed with a scotchpad , but because the areas underneath the shards are not properly etched and your etching remains "faint"
You can fill the etched areas with silver or white rub n buff which gives a much better effect but is not ideal.
Ideally you want to blast the glass , and that requires you to laser a mask on the glass , blast it and then remove the mask , a double process and a schlep , but the effects are WOW.
However all is not lost. The reson you get the shards is that the laser doesnt actually work on glass , it superheats the imperfections and microscopic bubbles and elements in the glass and cause the glass to heat fracture.
The problem is that you are not in control of the fracture and you cannot localise the laser pulses effect.
now there are various strategies that might work to minimise this
1) Put damp toilet paper over the area you are lasering , this serves to minimise any heat transference beyond the spot you laser and will not allow the glass to shatter uncontrollable - downside is the paper dries out and air assist will blow it away
2) Coat the glass with undiluted dishwashing liquid and allow to dry before lasering , this has more or less the same effect but due to a different cause, what this does is "damp" the glass , ie not allow the vibration of the shatter to extyend beyond where you are lasering , plus of course it does act somewhat like a heat sink.

3) Try different strategies , for example convert solid areas of fill or the whole graphic to greyscale , what this does is NOT give solid areas to engrave , where there is a fortune of heat affected zone damage , but will give pixels to engrave , ie tiny islands with some clear around em , the eye wont see it as anything but solid.
Generally LOW dpis and higher power work better on glass then high dpi's, but thats not cast in stone.

So experiment a bit and combining these strategies you should get an engraving almost identical to blasting or at least minimise the shard thing.
The shard problem also has another effect , it allows tiny sharp particles of glass to float around in the laser , not a good thing for mechanicals etc.

I would ALWAYS engrave in reverse from the back and have the clear side forward , even doing that and just filling the glass with paint/wax/rubnbuff will be far better looking at the back than having it facing forward.

Mike Null
11-10-2007, 5:51 AM
I'm with Rodney on engraving from the back. But I think you can avoid the glass chards altogether by reducing your power and resolution to the point that you are etching the surface rather than causing the micro-fractures.

I usually use two passes at 300 dpi.

Jim Huston
11-10-2007, 6:17 AM
A couple of thoughts---
1. The cheaper the glass the better it engraves! Many techincal reasons but it works that way. Jade glass is great! Lead crystal bad!
2. I use a PPI of 333 and one pass, 80 power and 83 speed on a USL 60 watt unit. Reverse engrave on back. Buff with green scotch bright.
3. Clean laser often!! I usually clean it every four hours when doing glass. Clean it good!! Every nook and crany.
JimH

Larry Bratton
11-10-2007, 6:52 PM
Jim hit it on the head. Glass creates this sticky dust that will fog your lenses in just a couple or 3 pieces. Check your focus lense often. I always engrave glass from the back also. Cheaper is the better.

Darren Null
11-10-2007, 11:54 PM
Actually, I'm doing some picture frames at the moment, and I'm engraving the front, at the customer's request. The engraving comes out clearer and more easily visible, for one. Also, the thickness of the glass gives a really nice drop shadow that makes the engraving stand out even more.

As to the fracture effect...I find that treating glass as a '150dpi' surface works for me. I burn at 300dpi, but normally only feed it 150dpi graphics, which still gives plenty of scope for tidy images.

George Elston
11-11-2007, 8:31 AM
Rodne touched on what I have found to be a critical point about grayscale. I do all my glass as grayscale and change all the 100% black to 80% black. This gives a defined point to the etch and the effect is amazing. It gives a precision to the engraving that is very different from sand blasting or acid etch, and the customers that are familiar with etching techniques love it and are amazed, the others just think it looks great. It also reduces the chipping and crazing as each laser blast point is distinct and separate from the ones next to it. The eye still sees it as solid.

Scott Shepherd
11-11-2007, 9:18 AM
Great point Rodne and George (about the greyscale). I have found that tip works a treat in a variety of non-glass materials as well. Any time something is giving me a fit I use that technique. Works very well on reverse engraving items that have a large footprint. A lot of times you get all sorts of inconsistant burn area because it's so much heat in that area, but going over to 70-80% makes it look much more uniform. A little different look, but it overcomes the problem with large burn areas.

I just posted a photo of something done that way in the Green Edge acrylic thread.

Bob Keyes
11-11-2007, 10:40 AM
Would someone like to elaborate on this "greyscale tip"? I am not familiar with the details. They would be much appreciated!!

Scott Shepherd
11-11-2007, 11:12 AM
Don't make things solid black Bob. That's the only technical way I can explain it :)

Here's what happens when it's not black, but rather some shade of it.

It makes evenly spaced little dots all over the image instead of constant overlapping burning of dots. I'll let someone else explain it, I'll just post the photo of an example :

click to enlarge
74988

George Elston
11-11-2007, 12:42 PM
In CorelDraw just pick your black objects and change them to 80% black, in PhotoShop it's a little more complicated. Use your eyedropper tool (the second one with the little crosshair target) and put a target on the blackest area of your graphic. Go to "Windows"--"show info". Go to "Image"---"Levels", and pull your middle slider over until the info says 80%. In Pshop you might want to select only your blacks first, depending on the content of the graphic. When you pull the levels over it effects ALL the levels and you might loose some detail.

I worked for years in printing and you NEVER used a 100% black in a halftone (it would look flat). We always cut it back to about 90-92%. Same holds true for etching. Control your dots and you control the visual depth of the piece. Etching at 100% black is like scraping off the top layer, and the piece looks flat. If you let it have a dot it gains character, not to mention the technical advantages mentioned by Scott.

I don't use photograve, I do my photo adjustments by hand and the first thing I do is set my whites and blacks (just habit). Blacks to 80% and whites to 5-7% (sometimes higher, your mileage may vary). The rest is pretty much as described many times in other threads (USM, contrast, etc.). But the point is don't use a solid black, and you need some dot in the white so it's not just "clear". Think of folds in a wedding dress, all white but darker areas and lighter areas, if the lightest areas are clear it looses it's depth, it just has holes in the etched areas.

Jim Huston
11-11-2007, 3:20 PM
Yep - I forgot to mention I use 80% black.

Shane Turner
11-11-2007, 4:12 PM
A question to those of you using the ~80% black method. What setting do you use?

Pete Thomas
11-11-2007, 5:37 PM
Hi David, in response to your initial question. I lightly rub the engraved area with 800-1500 grit sandpaper which removes/cleans up the sharp glass. Use a wet/dry sandpaper and only a very very light pressure. The end result is a nice smooth surface.

I also find that the cheaper glass does not leave that much of a shape glass surface and does not need much clean up.

-pete

Nicole Hernandez
11-11-2007, 5:40 PM
So you peaked my curiosity, what are you putting on this glass?

Bob Keyes
11-11-2007, 6:00 PM
Thanks George. I'll try that. Makes sense to me, so now if I can get the good results!!

Thanks again.

Mike Null
11-11-2007, 9:21 PM
Shane

You have the option in Corel Draw to set colors at various percentages. On the default RGB palette all percentages of black are shown.

David Hicken
11-12-2007, 3:13 PM
Thank you for all of your help on the topic. We tried the scotchpad and it worked great for removing the shards. So I guess at this point its really up to the customer if they would rather the etching be on the outside, or be reversed and placed on the inside. We've been etching glass at 250 DPI, 70% power 40% speed on a 30w PowerSHARP with only one run. It does an awesome job with clipart, but we just aren't really satisfied with the "Gray 3D" portrait etching. If you look at the image etched from different angles, you can see all of the detail, but looking strait on, its not very distinguished. We played around with different speeds and power and found with less power or more speed, some of the detail was getting missed all together. We probably wont be doing a lot of portraits on glass, but expect to be etching portraits on marble which I suspect will be similar to etching on glass. Any tips?

Thanks,
David

Mike Null
11-12-2007, 3:59 PM
I have found that marble will produce a much better image than glass. For some reason glass doesn't reveal shades of gray as well as other materials. I don't attempt portrait type images on glass.

One thing you might do is manipulate your image in photopaint to get better contrast before engraving.

Shane Turner
11-12-2007, 4:25 PM
Shane

You have the option in Corel Draw to set colors at various percentages. On the default RGB palette all percentages of black are shown.

Sorry I wasn't clear there. My lack of knowledge is not with Corel, but the laser settings that give the best impression when using less than 100% black.

On my Epilog I currently use 100% black, 600dpi, 45 speed and 100 power, with damp paper. I get a good contrast and get nice solid fills and sharp lines. But as you can imagine, at that DPI and speed it takes quite some time.

I was wondering if you got a speed improvement using 70%-80% black. Can you get away with a faster etch?

Mike Null
11-12-2007, 5:23 PM
You can increase your speed dramatically by reducing the dpi. You may even get a better image.

Bill Cunningham
11-12-2007, 10:02 PM
I have found that marble will produce a much better image than glass. For some reason glass doesn't reveal shades of gray as well as other materials. I don't attempt portrait type images on glass.

One thing you might do is manipulate your image in photopaint to get better contrast before engraving.

Glass is a very low res. medium (even lower than most wood).. Any photograph below 2" x 2" will leave a lot to be desired. Marble on the other hand, is a very High res. material capable of reproducing accurate photos as small as you can process them.. In photopaint, I use the brightness/contrast/intensity control to pre-process photographs, and always get pretty good results particularly on low cost glass as been mentioned

Stephen Beckham
11-12-2007, 10:25 PM
David,

I do portraits on glass ornaments for Christmas. I use 150 DPI images and burn them at 300 DPI on the laser. I usually use 1/3 speed of power. I say 1/3, because sometimes I'll slow down the laser, but reduce the same ratio of power.

Honestly - I can't see more than three shades of grey on the glass. So if you are looking for a pure image, it's not going to happen. Take a piece of sample glass and make up some greyscale charts for a test burn. See attached sample...

I used it to see where I could really tell the difference with my eye. I found that the bottom grid really worked for me - I could see the difference in each. If you can't see the difference at least on the bottom line - you'll never see the poitraits.

One of the things I do with every photo is take out the background and leave only the people. The contrast is greatly reduced from photograv having to figure out what is the darkest and what is the lightest color grey. I also raise my Gamma by 2-3% to make the image look faded - especially when the target has black hair (remember - darkest to lightest colors is what the software is compairing).

Another option - I can send you a couple small bmp files from my greyscales that have worked for me. You can give them a shot and see which work for you and go from there. Also - I added the CDR I tested with... You can shrink it as needed for size of glass...

Thoughts????