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Carol Barbero
05-05-2009, 9:53 PM
Okay, I'm ready to do a graduation announcement for my nephew on black acrylic. It has the school logo, a photo of him, and text. Do I need to invert anything or should it be "normal" engraving. Also, the picture is a color pic, would I be better off changing to gray scale. I'm such a novice!

Thanks in advance
Carol

John W. Love
05-05-2009, 11:05 PM
Carol,
I haven't done any engraving on Black Acrylic, but you will need to convert it to grayscale. Are you using photograv or are you manipulating the picture yourself? I am assuming you are engraving on the front since it is black Acryllic. Is that correct? If you are manipulating the photo yourself you may want to look through some of the threads on here on engraving on marble or granite because there is some excellent advice on how to get your photo just right by lightening and darkening different areas.

Rodne Gold
05-06-2009, 2:54 AM
You have to invert when engraving on black , the laser engraves all the "black" in the picture.

Chris J Drew
05-06-2009, 6:25 AM
Hey Carol.

You can get more control over the result by converting to 1-bit in Corel-Draw, rather than relying on the Epilog driver to interpret your greyscale.

In Corel, select your image & choose "Bitmaps/Mode/Black & White (1-bit)..."
Select the "Stucki" dithering pattern & adjust the slider to tweak the result, you can pan around your image & check the preview.
Pay attention to where you have black-to-white gradiends or detail in your image, you always have to "juggle" how much to lose during the conversion.

This method is much better than converting to a greyscale & then having the driver do the dithering ( even though the "Stucki" dithering in the Epilog Driver is very good, for photos you need more control over how the dithering is applied to light & dark, gradients & details etc )

You can get better results by experimenting with adjustment of brightness & contrast of the image before doing the conversion.

Good luck!

Chris.

Frank Corker
05-06-2009, 6:52 AM
Yes it needs to be inverted. If you decide that you want to remove the background before inverting it, then it has to be black because when you invert it, the black will turn to white and won't engrave.

Carol Barbero
05-06-2009, 9:50 AM
Thank you all for the advice. I'll give it a try tonight!

Brian Robison
05-06-2009, 10:32 AM
And make sure to use cast acrylic.

Steve Clarkson
05-06-2009, 1:54 PM
Not sure......but I think all colored acrylic is extruded......no one that I bought acrylic from has ever confirmed it......they just say they don't know.

But the only time it really makes a difference is on clear acrylic.

Brian Robison
05-06-2009, 2:11 PM
I've buy extruded acrylic in black.
I use it all the time as a back piece for my license plates.

Rodne Gold
05-06-2009, 2:16 PM
Burn a piece , cast burns with a crackle and wont drip molten flaming balls , extruded will burn silently and drip molten flaming balls

Brian Robison
05-06-2009, 2:23 PM
Ouch! That's gotta hurt.

Mike Null
05-06-2009, 2:48 PM
Steve

Check out Rowmark colorcast acrylics in the Johnson Plastics catalog.

Larry Bratton
05-06-2009, 2:52 PM
Not sure......but I think all colored acrylic is extruded......no one that I bought acrylic from has ever confirmed it......they just say they don't know.

But the only time it really makes a difference is on clear acrylic.
I buy cast colored acrylic from Piedmont Plastics regularly. Just because it is colored doesn't mean it's extruded.

Frank Corker
05-06-2009, 3:53 PM
I have about 2 tons of different coloured acrylic. All of it is cast. I actually don't have any of it which is extruded.

Rodne Gold
05-06-2009, 4:09 PM
Degussa who supplys Euro and africa make a huge range of extruded colours and others
Extruded will stress crack with solvents far more than cast
Extruded is generally far tighter in thickness tolerance than cast - cast can vary by more than both plus and minus 10-20% over a sheet.

Carol Barbero
05-06-2009, 4:17 PM
This is the piece I'm going to attempt to put it on.
http://www.laserbits.com/index.php?main_page=product_info&cPath=65_366&products_id=1012

They indicated that the entire engraving area is acrylic with a black plastic backing.

I'll let you know how it goes tomorrow. The whole photo and inverting thing just messes with my head!

Brian Robison
05-06-2009, 5:20 PM
Oh, you'll be fine.
too bad you don't have some practice black cast acrylic.
Are you in Wilseyville, Ny? Maybe West Spencer?

Carol Barbero
05-06-2009, 5:30 PM
Brian:
No I'm not. Thanks for the help.

Brian Robison
05-06-2009, 5:37 PM
Too bad, I was going to offer up Steve to help you out!:D

Tim Bateson
05-06-2009, 10:23 PM
The whole photo and inverting thing just messes with my head!

You'll be engraving the back so the picture needs to be flipped so it looks correct from the front. Another way to look at engraving on black is you need to engrave a negative and on white you engrave a positive image.

Barbara Sample
05-13-2009, 12:42 PM
You definitly need to change the picture to greyscale. I use photograv to process my photos so I am not positive how to do it otherwise. I do think you have to invert it but am not sure. Try it on a small piece and engrave at 300 dpi auto ppi, see if that works for you. I have a 30W machine and I use 40 power 100 speed.
Good luck, Barbara

Chris J Drew
05-18-2009, 7:28 AM
You definitly need to change the picture to greyscale. I use photograv to process my photos so I am not positive how to do it otherwise. I do think you have to invert it but am not sure. Try it on a small piece and engrave at 300 dpi auto ppi, see if that works for you. I have a 30W machine and I use 40 power 100 speed.
Good luck, Barbara

I don't know about Photograv but if you're not using that then you definately don't want to convert to greyscale.
Convert photos to 1-bit black&white using the Stucki dithering within Corel Draw.
This bypasses the driver's conversion dithering & gives you more control.
If your image needs scaling then do this before converting to 1-bit.

PPI doesn't apply to an Epilog machine, the nearest thing to PPI on the Epilog is Frequency, but that only applies to vectoring, not rastering.

Only invert your image if the lasering has a lightening effect on the material.