Suggestions on improving engraving on black granite?

[Brent Franker]

Hello!


I'm a novice laser user and still figuring this thing out. I have an Epilog 36EXT 75watt. I tried my hand at laser engraving a black granite tile for the first time the other day. I used PhotoGrav with their recommended settings. It came out just "OK" to me and seemed a little dark. Without spending a bunch of money experimenting too much, I figure I'd ask you guys what the best way to increase the brightness of the engraving? More power? More resolution (did 300 dpi)? Feed PhotoGrav a picture that I actually make lighter/brighter first? Any recommendations from the pros? I did change the resolution of the picture to 300dpi and sized it exactly the same as I needed it in Photograv so I didn't do any stretching or anything like that after processing the photo.


Here is my original picture.
Eric Lesage2.jpg

Here is what Photograv "estimates" it should look like (ignore the black backgrounds and text, I added that for the customer).
132013337_420492635674786_4630085148348256947_n.jpg

Here's the finished result. This picture actually makes it look brighter than it does just holding it up and looking at it. It's in a bright room too. Finished black granite below...
PXL_20201219_011030817.jpg

And here's another example... same 300 dpi and same settings recommended by Photograv which was 100% speed and 52% power.

Original picture
Kim Windle.jpg

Photograv estimate
Kim Windle (GRAY).jpg

Finished tile. Again, the darn camera actually improves what they look like as compared to looking at them with the naked eye... they are a bit darker.
PXL_20201221_184633222.jpg

I've seen some YouTube examples of a guy engraving on these $5 12" black granite tiles at 300 dpi using just what Photograv gives him and his final results look like a black and white picture and incredible?!?! Anyway, just wondering if any of you had some recommendations as to the best way to get these to come out a little "brighter"? Thank you and Merry Christmas!

[Kev Williams]

I've never been able to make black granite white. I know (from readers here) that black MARBLE goes fairly white...

Try this on the next piece of granite...

Before engraving, wax it with car wax. Couple of coats, get it real slick--

Engrave

Spray paint flat white, let dry overnight---

The paint on wax should be (<<SHOULD be**) fairly easy to remove.

My way: you need some denatured alcohol, some an cotton sheet or T-shirt you can cut up, and a good sanding block (hard rubber one works great)
cut the cloth big enough you can hold it tight around the sanding block, wet the cloth a bit with the DNA, and watch the magic happen

--change out the cloth as needed...

[Keith Outten]

I shared some information here years ago about coating black marble tiles with Amour All before you engrave. It works, makes the engraving much lighter. I have not tried it on granite but it may be worth a try. I am not much of a photo engraver but I have engraved a truck load of college diplomas for parents since they don't get to keep the diploma that helped pay for

[Brent Franker]

Ahh... I'll give that a try, Kev! I'm thinking this will only be acceptable though for pieces that will remain inside and not be placed outdoors because the paint probably won't last all that long unprotected on the granite. For inside stuff I can see how this would really make the lighter areas pop. Thanks!

[Brent Franker]

Thanks, Keith! I'll give that a try too. Your examples look amazing! Thank you I do have some tire dressing here but not the Armour All brand but will go pick some up to try

[Brent Franker]

Just an update. I ended up spending a couple hours "playing" around with this and different settings. I tried the Armor All trick but, no difference on black granite. Dang! Didn't try the paint trick yet but will do that later when I have a bit more time

But, I was able to get better results by using PhotoPaint on the picture first and then using Photograv. What I did that worked best was converted it to a 16 bit grayscale then did the "tone curve" on it and pulled the center of the diagonal line to the upper left about 3/4 of one square. That brightened the image pretty good without losing too much detail. I tried 1/2 and even a little over 1 square but at pulling the line 3/4 of the way seemed to be the best compromise. I remade the customer's piece (cost me another $5 but it was worth it!) and they were happy

For any other new users out there, I found a tile at Lowe's with chipped edges and they marked it down to $3 for me so that was test tile! Unfortunately, the lady at the register screwed up and charged me full price and I didn't notice until I got to my car. Then, the line at customer service was too long to justify $2 so I just sighed and went home. LOL

Anyway, here is what I did in Corel...
Granite examples.JPG

It came out like this...
PXL_20201224_192439281.jpg

Oddly, the simple inverted grayscale image I tested wasn't all that terrible. Photograv is better but doing just a simple "invert" on a grayscale image was not terrible!

I also remade the gift for my fiancée and it came out very good too! Thanks for the recommendations!
PXL_20201224_191023897.jpg PXL_20201224_191040232.jpg

One thing that was odd during my "adventures in lasering" yesterday was that I noticed I was using Photograv 3.0 and saw that 3.1 was available. In order to rule out everything, I decided to see what it took to update mine. The guy there got back to me very quickly and said it was $25 and he could email me a download link. In talking to him, he said none of the processing changed (dang!) but they just added material. Ok, still cool. BUT, what I noticed was using the same photo with the same machine and setting in Photograv, it greatly changed the power recommendation??? In 3.0 it told me 100% speed and 52% power. In 3.1 it told me 16% power and 100% speed. What the??? For the heck of it, I tried it and that's the black square in my test tile you see above... basically didn't do squat. I ended up with going with 100% speed and 57% power. I was under the impression that none of this should have changed? He said the only difference was they added material... but, I know that's not accurate because the bottom pane changed, menu layouts changed, a lot more changed than just material. Anyway, was curious if any of you noticed that 3.1 gives you WAY LOW power suggestions compared to 3.0 which was pretty close? I double checked everything and I have selected the correct laser and power so not sure why 3.1 is so "bad" all of a sudden at the recommendation?

Thanks again!