Canvas Woes

I’m working on a series of projects inspired by some of the canvas art seen here. I’m having issues getting things lined up properly. First off images I send to the machine are making lines across the print in both directions.

As for the canvas issues, I’m having a hard time getting them dark enough. Also there’s a lot of unevenness in the way its engraving. At first I thought it was the way the canvas was painted but when I tried it on a scrap coaster it does it there too. They engrave looking good (minus the vertical lines) but they’re faint. It doesn’t matter if its on raw or painted canvas its very faint. Does anyone have any suggestions on how to get darker without just burning straight through the canvas? I really love the projects on here and they’ve inspired me to do some of my own. Any suggestions anyone has would be greatly appreciated.

Settings I’m using are:

Speed: 1000
Power: 40
LPI: 270

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How are you preparing your photos?

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and how are you preparing your canvas?

Most of the art on here involves spraying spray paint onto the canvas and then engraving the white parts off…it looks like you’re just engraving right onto the gessoed material.

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I’ve tried on the canvas straight, and brushed on acrylic paint. The photo of the canvas above is the acrylic based paint done in a couple layers, full black dried, then white, then an invitro gold and invitroviolet mixed.

I’ll try the spray paint method tomorrow, haven’t had a chance to run to the hardware store.

I’m prepping my photos by simply adjusting brightness, contrast, saturation, etc. The photo itself doesn’t have those lines.

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Those lines you are getting I think has to do with your LPI and variable engrave. They tend to be that way below 450 LPI and the second problem shows up when there is a very low power setting as you are dividing a power of 40 by 254 for each level of gray. Even at 100 power each shade of gray is getting less than half a number (%?). Of course, full power and high LPI is extremely hot, so how to cool it down? The only variable left is speed, and top speed is different for each level of machine, Basic, Plus, or Pro. 4000 speed on a pro seems almost useless except in the most delicate situations but that is what your situation is, though you will have to test with bars that go evenly from black to white on some sacrificial canvas that it does not go heavy on either end of a gradient.

That brings up a deeper problem with the image. There are few grays where you need many. The blanket on the horse is going to be hard to pull off as there is little variation from black and at the other extreme while the white face has a bit more definition, but blends right into the snow. Normally, it is hard to get enough contrast but in this case, you need more definition away from the extremes. Under the best of conditions, this photo would be very difficult to get, and if you had a color photo I would be changing say a blue blanket to yellow before going black and white to increase that definition. (the manipulation of colors before going gray is rarely suggested, but the more data you can control gives you better control) If the blanket was already black there would be little definition to bring out.

I once had a plugin that detected texture that they actually brought out a polar bear in the snow as an example but that was many computers ago.

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Sadly, some materials simply don’t get that dark on their own. Most fabrics seem to fall in that camp.

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I have read that a Borax and water mixture applied to the surface and let dry will cause engraves to be really dark. I also read that you have to increase the speed quite a bit with this method as it tends to burn deeper also.

It takes a lot of experimentation to get it just right.

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I thought the borax and water was for wood? Do you think it would work on gessoed canvas?

My suggestion would be to buy black canvas and spray paint it white. This will give you a much darker image with less power .

CONDA Black Canvas Panels 8x10 inch, Pack of 14, 100% Cotton Acid-Free, 8 oz Gesso-Primed, Art Boards for Oil & Acrylic Painting

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I’ve never tried it on canvas… but you might look into applying a wash of water/borax to the canvas. I will make the pew-pews almost totally black. There’s a sweet spot in the borax dilution though I think because if you have too much borax it will just be a bunch of black soot.

He’s just processing the image for the first 14 and a half minutes so you can probably skip to that point.

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I have this photo in color. It is a black blanket to begin with maybe I can photoshop it to a grey color. As for the white on snow? How would you go about adding more definition so its clearer? I’m expecting to have several sacrifice pieces to get it right. Everyone on the forum is incredibly helpful.

We’re running the glowforge pro. Is there a table somewhere to help determine what the higher speeds do to the power of the laser? I.e. 2000/100 is equal to 1000/50? From the little amount of tinkering I’ve done at speeds over 1000 it seems to be on a somewhat unpredictable curve.

I will run this with higher LPI and see if that gets rid of the lines. I’ve got to go by the store later today anyway and will pickup some black canvas to try and some spray paint.

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The power is the power. If you increase the LPI you increase the power per area. If you increase the speed you reduce the power per area, so if you max out the other two it will take a pretty high speed to bring the amount of total energy applied per area down. With the higher speed, the head has to slow down after each pass so that narrows the area a lot and the slowing down part can take longer than the engraving part to the weird effect that faster speeds can take longer than slower speeds depending on how wide the engrave is. There is a sweet spot where it takes less time before increasing it but I’m looking at the result more than how long it takes.

For a pro, the top speed is 4000 which would allow you to even go to 1355 LPI. It will take very long but be amazingly smooth.

As for the photo itself, the blanket being black to start with makes things difficult. If you can isolate the black with a mask, max out the color saturation, make it lighter, and then increase the contrast there, you might be able to pull some detail, rather than have a black splotch in the middle. (a big gray splotch in the middle would be little better) Likewise, if you can isolate the white parts of the horse, darken it a bit, and increase the contrast there, but keep it all a bit darker than the snow next to it, you will make it easier to see what is head and what is snow. :grin:

Edit: In Gimp if you set the discrimination to zero, it will pick only that exact color, but as you pull the mouse down the discrimination range increases, so if done slow enough, you can see exactly what will be included and stop exactly at the point that you only get exactly what you want. That little trick has changed the world in terms of getting the mask I want, and then I use Feather for a few pixels so what you change will not be all jaggy.

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Adding borax made a tremendous difference. The material didn’t burn through but the darkest areas have no structural integrity left to it. Guess the speed needs to go up some still.

Speed: 1400
Power: 60
LPI: 450

Upping the LPI definitely solved the issue of random lines across the print. I’m learning a lot from this process. The photo editing may be above my head right now but I’m just going to keep trying until I figure it out.

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Definitely a learning process.

Is there a way to seal or protect the engrave to prevent it from falling apart?

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Are you willing to post the original image? One of us may be able to help with the editing.

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Looking much better! I would try for4000 full power 675 LPI (or even 1355 LPI) after fixing the location very well. It may come out too light but if you do not move anything and the work is firmly in place, you can run it as many times as you like without ruining the canvas, whereas when it is too slow, the material is trashed.

That would be very helpful although I still need to figure out how to fix it regardless.

I’m not sure how I’d seal it to hold it there. It’s near tissue paper thin/fragile in the dark areas.

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If you have GetPaint.net then the V2 of this will open in layers and you can see how I treated each of them differently. If not, then V3 may engrave better! :slight_smile:
Horse.zip (1.2 MB)

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I did this with Gimp…

The Image and Gimp file are here if you want to see what I did,
Winter-horse.zip (3.4 MB)

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