If you've got the xTool M2 and you're wondering which module is best for engraving photos on slate, I've tested all three: the standard 10W diode, the 20W diode and the 3W infrared. Same photo, same coasters, same machine. The only difference is the laser module that made them.
In the video above I make it a blind test, so have a guess before the reveal if you like. Below is the written version: how I tested each module, the final settings for all three, which one came out best and why, and a few tips that work whichever module you've got.
Jump to: Keeping it fair · Broad test grid · Reading a grid · Narrowing it down · Line density · Final settings · Which module won · Why they're different · Slate tips · My verdict
Why I tested this
In my last M2 video I engraved a photo onto slate with the infrared module, and it came out really well. Since then a lot of you have asked the same question in the comments: can the normal blue diode modules do that too?
Most people with an M2 have the 10W module, and some have the 20W. So I wanted to find out what each one can do on slate if you give it the best possible chance. The obvious question is whether more power gives you a better photo. The 20W has twice the power of the 10W, so you'd expect it to do better.
Keeping it fair
I didn't just use the same settings on all three. A setting that works for one module won't suit the others, so that wouldn't tell you much. Instead, each module went through the same four steps:
- A broad test grid to find the right area.
- A closer test to narrow it down.
- A line density test.
- The final photo with the winning settings.
Everything else stayed the same: the same round slate coasters, the same photo at the same size, and the same image settings in xTool Studio.
Step 1: the broad test grid
If you've not done one before, xTool Studio has a tool for this called the Material test array. It lays out a grid of the same photo, each one at different settings.
- Open Material test array in xTool Studio.
- Pick Power for the X columns and Speed for the Y rows.
- Set the max and min for each, and how many columns and rows you want.
- Make sure the grid fits on your slate before you send it.
This is the broad grid from the 20W, running from 30 to 60% power across the bottom and 300 to 600 mm/s up the side.
When I fitted the 20W, the M2 asked me to run a one-off calibration before it would start. It took me a couple of goes to get it to finish, but once it was done I didn't have any more trouble. Worth knowing if yours does the same.
How to read a test grid
With the grid engraved, I'm looking for the squares where the face has the best range, from the darkest shadows to the brightest highlights, without the detail burning out.
- Too much power or not enough speed: the light parts of the face turn into flat white patches. The cheek and the forehead merge into one and you lose the shape of the face.
- Too little power: the whole photo looks faint and gray, like it's been drawn on the slate in pencil.
- The one you want sits in between. The highlights are bright but you can still see texture in them, and the shadows under the hat brim stay dark.
If two squares look close, pick the one where the eyes look sharpest, because that's where people look first.
Step 2: narrowing it down
Once I had an area I liked on each grid, I ran a second, tighter test around it. Smaller steps in power and speed, so I could find the best combination rather than the nearest one.
This is where most of the time goes. Some of these slates only had a handful of photos on them, but each one tells you a bit more.
Step 3: line density
The last test is line density, which is how close together the engraved lines are. More lines per centimeter can give you more detail, but it also puts more heat into the slate, and if you go too far the photo starts to lose its contrast.
So I took the best power and speed for each module and tried it at a few different line densities, to find the one that held the most detail. The one above is the 10W at 150, 160, 170 and 180 lines per cm.
The final settings for each module
With all of that done, each module got its own winning settings for the final coaster. These are the exact settings I used, and they're the same ones in my free xTool M2 laser settings page.
| Module | Power | Speed | Lines per cm | Passes |
|---|---|---|---|---|
| 10W diode | 42% | 360 mm/s | 160 | 1 |
| 20W diode | 40% | 400 mm/s | 170 | 1 |
| 3W infrared | 84% | 107 mm/s | 160 | 1 |
All three used Jarvis dithering, one pass, bi-directional engraving and the same air assist (15%). I set the material to Rock Stone and used Auto Adjust in the image editor to invert and optimize the photo (more on that in the tips below).
Treat these as a starting point. Slate varies from batch to batch, so run a quick test on a spare piece first. You'll find these and nearly 300 more tested settings for xTool machines in my free Laser Settings Library.
Which module did best?
Before I tell you which is which, here's how they look if you didn't know:
- B stands out straight away. It's the brightest of the three, the whites are cleaner, and there's more contrast in the face and the jacket.
- C is close behind. The face is sharp and you can still pick out the detail in the hat and the stubble, but it's not as bright as B.
- A is the softest. It's still a good result, but some of the fine detail in the face and the hair has gone, and it looks a bit flatter.
So B, the brightest one, is the 3W infrared. C is the 10W. Which means A, the softest of the three, is the 20W.
I did have a feeling the 10W might edge it, but it's still a surprise to see the lower power module come out ahead.
Why they're different
Put the 10W and the 20W side by side and you can see where the difference is. Look at the eyes, the stubble and the texture on the jacket. The 10W holds on to those small details, and on the 20W they start to blend together.
That comes down to the laser spot. The 10W's spot is smaller than the 20W's (xTool's spec is 0.06 x 0.04 mm for the 10W and 0.08 x 0.06 mm for the 20W), and a smaller spot can hold finer detail.
Compare both of them to the infrared and the gap is much bigger. The infrared is a different kind of light to the blue diodes, and slate reacts to it differently. You get a brighter, more even white mark, and that's what gives it the contrast.
Look at them from an angle
The biggest difference shows up when you tilt them. Looking straight on, all three look decent. But as soon as you look from an angle, the 20W almost disappears, the 10W goes dull and gray, and the infrared stays bright. That's how you'll see a coaster most of the time, on a table, from the side.
How long each one takes
Based on the estimates in xTool Studio for the same design, the 20W was the quickest at about 18 minutes, the 10W took about 24, and the infrared was the slowest at around 33 minutes. So the slowest module gave the best photo, and the fastest gave the softest one.
Getting the most out of slate, whichever module you've got
- Invert your photo. The laser turns slate a light gray, so the engraved parts become the highlights. If you don't invert it, you end up with a negative.
- Use the Rock Stone preset and Auto Adjust. In xTool Studio, set the material to Rock Stone, then use Auto Adjust in the image editor. Between them they do most of the inverting and tidying for you.
- Let the M2 measure the height. Slate isn't perfectly flat and no two coasters are the same, so measure each one rather than typing in a number.
- Pick your flattest coasters for photos.
- Test on the same batch. Run a small test grid on a slate from the same pack before you do the real thing. It costs a lot less than a ruined coaster.
My verdict
All three of these are good results, and I'd be happy giving any of them to someone. But the infrared is in a different league. My scores:
- 3W infrared: 9 out of 10
- 10W diode: 8 out of 10
- 20W diode: 7 out of 10
If you've got the 10W, you can get a really nice slate photo out of it with the right settings. If you've got the 20W, it'll still do a good job, it's just not what that module is best at. And if slate photos are something you do a lot of, the infrared is the one to get.
If you want to see the full infrared process from start to finish, my first slate video, How to Engrave Photos on Slate with the xTool M2, walks through it step by step.
Did you guess right?
Let me know in the comments on the video which coaster you picked for which module, and which material you'd like me to test on the M2 next. All the settings from this guide are on my xTool M2 laser settings page, free.
