41 – Photo Engraving Slate and Granite (25:13)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Laser Engraving Machine. Thinklasers Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ shows us photo engraving slate and granite.

Photo engraving slate and granite  - tiger image
Photo Engraving Slate and Granite – Tiger Image


You can’t cut minerals like granite and slate with your laser.
Description of Foliated Metamorphic Rock
Test pulses on different slates and granite and examination of results.
Production of glass by melting of the surface.
Testing different settings to see what size dot one can produce on slate.
Examination of results.
Comparison with wood/card technique.
Trial engraving on slate.
Seeing the picture created has less contrast as it is only shades of grey.
Use of furniture polish to enhance the contrast.
An experiments engraving the photograph on a different slate and granite.
Changing the configuration to get better results.
Using Briwax to enhance the results.

My thanks go out to Tom at Thinklaser for giving permission to embed these videos on this site. If you are looking for a new laser machine from a quality supplier, then I would suggest you check out their website: www.thinklaser.com.

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Transcript for Photo Engraving Slate and Granite

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0:14Well welcome to another Lightblade Learning Lab. What we’re going to talk

0:19about today is mineral materials and I’m afraid we won’t be able to cut those, we

0:25shall only be able to mark them. But we need to understand a little bit about

0:30the material itself before we dive in and try and do something with it.

0:36First of all, we have to understand we can’t cut it, but I think that if I gave

0:41you a piece of granite and this machine, you would never attempt to cut the

0:44granite. You might not even think you’ll be able to mark with it, but we can. Now

0:52as I’ve told you many times before, I’m an engineer, so I will not pretend to be

0:58a geologist. Although I have to admit to having a passing interest in many

1:03aspects of geology. So what we’re going to talk about today is something called

1:06foliated metamorphic rock, come on in and I’ll show you what we’re actually

1:16talking about. Okay, so now I think you’ll recognise what I’m talking about,

1:21something we all recognise as slate. It has got some strange properties, in that it,

1:30as you can see here, it tends to flake and it’s used for roofing tiles for that

1:34very reason, it’s got flaky properties. That flaky property comes from a

1:39material that’s probably built into most of these called mica, which has got this,

1:45it’s got little shiny bits in it. So if we look closely at the surface of these

1:50various types of slate you’ll find little teeny-weeny shiny crystals in it,

1:55and that’s the mica. But in addition to that it’s also made up of silicates,

2:01which are like sandstones very fine sand materials. It’s basically a

Transcript for Photo Engraving Slate and Granite (Cont…)

2:08sedimentary rock that was laid down millions of years ago in the bottom of

2:11an ocean, layer upon layer, and then it’s been compressed by huge pressures as

2:17it’s been subducted under further rock formations, and it’s pressed it into this

2:24rock. So it started off as silt and now it’s become metamorphosed, which is what

2:30this metamorphic bit is, it’s been changed into a rocky material, a stone. So

2:36the main producers of slate in the world are; this is from Spain, this is from

2:42China. It comes from North America and it comes

2:46from Brazil, we would know in the UK, a big slate producer as being Wales. Well

2:53it’s big in the UK but it’s not necessarily big in world production, but

2:58these two items here are both Welsh slate. But let me just do a couple of simple

3:04tests on this slate and we will see if they are all the same. Now I’ve got full

3:13power operating through the lens there and I’m going to hold a pulse on for

3:19probably two seconds. Nought, one, two. The Chinese slate, nought, one, two. You

3:28notice the difference in the colour of the burn and also the fact this was

3:31rather sparkly. Now here’s a piece of green Welsh slate

3:37Nought, one, two – and here’s a piece of Welsh plum slate, nought, one, two. Let’s just go and take a

3:47look at these under a microscope and see what we’ve done to this material.

3:51Well first of all, the Spanish slate. You can see the way that the edge has

3:57started to flake away, now you can also see this glassy volcano effect around

Transcript for Photo Engraving Slate and Granite (Cont…)

4:03the outside here. Let’s just try and chip that off. So this is a particularly

4:15unstable material to work with, it’s all flaky. Where did the glassy material come

4:21from? This was fairly high in silicates this material, when you heat silicates up

4:26to a thousand degrees C they become a liquid, a bit like syrup, and then when

4:32you let them cool well you get glass and that’s what we basically created on the

4:37surface there. A little, a little volcano of glass around the edge and if we look

4:41carefully here you’ll see that not only did we produce a volcano of glass,

4:45there’s a little bead of glass that’s come out of the volcano. That’s a

4:49starting point for Spanish slate, doesn’t look like a very stable material does it?

4:53Let’s take a look at our Welsh plum slate, you can probably see it I think,

4:57that this edge round here is flaked up. Just here, and here we’ve got our glassy

5:04material again. What have I just done? In fact it wasn’t a glassy material, it was

5:10a glass bubble which I’ve just burst. Look there’s the little teeny-weeny

5:14flakes of it. You should look as we dig it into there,

5:19that’s glass all the way. Let’s look at the Green Welsh slate.

5:29Again, we’ve got our glassy structure on the surface here, look I’ve got a little glass

5:33balls ejected from the volcano and let’s see what we can do with this. Can we peel

5:38this glassy subjects substance off the surface? It’s slightly more crumbly glass

5:43than the other and finally we look at the Chinese slate. There are lots of

5:47little white spots, now those little white spots are reflecting the light and

5:53they, we don’t appear to have any glass formation here. So there’s a very high

5:59mica content in this material. Now mica melts at about 1600 degrees C, whereas

Transcript for Photo Engraving Slate and Granite (Cont…)

6:09glass forms at about a thousand degrees C. But under normal daylight viewing with

6:15an eye glass, I can in fact see that this hole is glazed all the way around and in

6:22fact there is a small ring of clear glass around the edge.

6:26It’s hardly perceptible but there is a very small amount of glass there. Well

6:32here we are at the first hurdle, we’ve already found out that not all slates

6:37are the same. I think the only thing that we can do, is to go back to my good old

6:45standard test and see what size dots we can produce on this material. Now while

6:51we’re here and because I can. I have a small sample of granite here, let’s see

6:59what granite does. Nought, one, two. That’s producing the same

7:06glassy volcano as the three slate samples that I’ve tested So we’re going to

7:10carry out our small test pattern which has dots point one of a millimeter apart

7:16and we’re starting off at quite a high speed 200 millimeters a second and 30%

7:23power. But bear in mind that this machine has been set up for special mode so it’s

7:29still got pulsing power on it. We’ve got a nice row of dots along the centre,

7:38we’ve got a joined row of dots across the bottom and these dots are whiter

7:45than the background. So it’s pale grey as opposed to a light grey, so there is a

7:52bit of a contrast there that we can work with. So we might be able to do some

7:58pictures with this, whether they’re just going to be engraved logo type pictures

Transcript for Photo Engraving Slate and Granite (Cont…)

8:02or whether we can actually get some photographic texture into it is

8:08going to be rather interesting. Well let’s see how the Chinese slate performs

8:12shall we?

8:17We can’t really see the individual pixels, so I think we’ll slow it down –

8:26let’s try 150, that’s a really nice line of pixels that just touch each other, so

8:38that’s point two diameter pixels, but they’ve got a little crisp holes in the

8:42middle of nearly every one of them. So maybe I should back the power off a

8:46little bit, see if we can get them even crisper.

8:54Well the dots are a little bit crisper but they’re also very faint, so I think

9:00we’ve gone the wrong way and I think we’re gonna have to stick with

9:04something like 30% and a hundred.

9:13Well I would say that’s a pretty good compromise, it’s a 125 millimeters a second and

9:2425% power with special mode and a 2 inch lens. So what we’re now going to do is to

9:32dig out my formula and calculate what the best resolution for the picture

9:38should be. Well I’m using my well-tried formula for photo engraving and we’re

9:43gonna try and adapt it to fit this particular material because this was

9:47designed for wood and card but we’ve got different parameters here on slate. I’m

9:54fairly confident this formula will work with a small amount of tinkering here

9:57and there. So from the little experiments we’ve just done, we found it the best dot

10:02that we can get is 0.2 and that means that we can keep, that means

Transcript for Photo Engraving Slate and Granite (Cont…)

10:08we have to keep the resolution of the picture at about a hundred and

10:11twenty-seven. Well, I’ve pushed the boundaries a little

10:14bit and I’ve pushed it up to a hundred and fifty, I’ve reworked the picture and

10:18I’ve done it at a hundred and fifty PPI. All this work was done originally with

10:23common mode, but because we’re using special mode where we’re able to use if

10:28you like half the power twice the speed and we still seem to be able to get a

10:34dot, because that’s how I’ve managed to find my dots. We’ve done that in probably

10:40something like 1.5 milliseconds, so what I’ve done I’ve nominally chosen 1

10:47and 1/2 milliseconds as my parameter here, instead of 3 milliseconds. That

10:53brings me down to 7.5 milliseconds per millimetre and when I divide that

11:007.5 into 1 second it means I actually can run at 134 millimeters a second. I’ve

11:07pushed the resolution up a shade, so what I’ll do I’ll pull the speed down a shade

11:12and run it at the test speed that we established we got the best dots which

11:16is 125 millimeters a second. So hopefully those 2 things will start to cancel each

11:22other out

11:27and the power that we found we can use is 25% / 25% in SP mode and that’s how we

11:36established our test pattern. The paperwork where you’re producing lots of

11:40smoke, we need to turn the air assist down so that it doesn’t blow back down

11:44onto a job. But in this particular instance, I think we need the air assist

11:48on and set to maximum. That’s how I’ve tweaked my formula this time round. Now

11:55we must remember that we had a black background here and we were producing

12:02white cuts and here on slate we’re doing exactly the same thing we’ve got a black

Transcript for Photo Engraving Slate and Granite (Cont…)

12:10background and we’re going to produce white cuts off it.

12:20I can’t smell too much in the way of fumes.

12:31Well there’s our end product and obviously that looks pretty good on

12:37slate, but to be honest when you look at it from a distance and compare it to a

12:42proper black and white image yeah it’s it’s a little bit weak, because the

12:50fundamental problem is we can’t get white, all we can get is light grey and we

12:56can’t get black, because all we’ve got is the background. So we’ve got a two shades

13:02of grey picture here, now I don’t know whether we can enhance that a little

13:06bit. So here we’ve got some furniture polish which will produce a slightly….

13:20so yes coating it with something does improve the quality of it, as you can

13:26see. Just a little bit of furniture polish has changed this from a

13:29grey to a dark grey and that has enhanced the blacks without actually

13:34taking anything away from the background.

13:38So that’s pretty good going for something like a hundred and fifty dots

13:43per inch.

13:48So the next question is, can we repeat that on Spanish slate?

13:57As you can see this, this Spanish slate is a different kettle of fish, it’s not

14:02very, um what can I say, it’s not very flat. It’s not very uniform. So I think

Transcript for Photo Engraving Slate and Granite (Cont…)

14:08we’re going to have all sorts of problems with this, but we’ll give it a


14:21Well from that angle there it doesn’t look too bad, catch in the right light

14:26it’s not too bad, but when you look at it in front like that it’s pretty weak and

14:32so look there’s the difference. Now at the moment that’s the difference between

14:37the two slates but I haven’t enhanced this one. This was just two shades of, it

14:42was a grey and a light grey. This one’s a dark grey and a sort of… a sort of a

14:48funny muddy brown. Well I think even though we’ve enhanced it I don’t think

14:55there’s any doubt that this is a much lighter background than this one, this is

14:58a much better slate to etch on than this. Because this is definitely blacker, the

15:07shades of grey on the slates are not that different, but it’s the composition

15:12of the slate itself which doesn’t give the contrast when you put these little

15:17teeny-weeny burn marks on. Now I say burn marks because I think that what we’re

15:21doing we’re actually hitting this so hard that we’re again evaporating little

15:25pits. We’re not producing the glassy effect, because we’re not giving it long

15:31enough to erupt and turn into Glass. I thought that this process on here would

15:36have been a stone chip process I.e. like on glass where we heat the surface of

15:42the glass up and we pop a little stone chip out. This looks to be much more of

15:47a burning process because when we look at this under the microscope you’ll see

15:53that there are definite uniform little spots not random shards. So we’ve already

16:02established that this material is going to work very similar to slate. Now I’m

Transcript for Photo Engraving Slate and Granite (Cont…)

16:06not going to change the settings I’m going to leave them exactly the same as

16:09they are 125 millimetres a second 25% power and well you know this is the

16:17same basic material even though it finishes up as a much harder and tougher

16:21material the basic structure of this material is still made from the same

16:25chemicals and elements. We’ll take a gamble on my one and only

16:30piece of material and we’ll give it a try. Now the great thing about this is

16:35we’ve got a black product to start with so hopefully the gray lines on here will

16:41give us a much better contrast when it comes to a picture.

16:53Now note that I’m doing all this work without any extraction on, there are no

16:58noticeable fumes at all with this.

17:04When we look at that under the microscope, we’ll probably find that we

17:09could’ve possibly increased the resolution, but I think when you look at

17:18it from sort of just a short distance away it’s still pretty amazing. I might

17:26pop down to my local stonemasons and see if they’ve got any reject granite that

17:30they could either let me have so that I could do some more experiments.

17:34I just noticed, one of the things that Iwas talking about and I can see on

17:39here…. now those little shiny crystals

17:41that are all across that vein there that’s the mica that I was telling you

17:45about. I catch them right, maybe you can just see that they’re shining in the

17:49light. That’s the mica, we’ll just go and look at these under the microscope. I mean

17:57we’ve got enough slate here to try another two or three so let’s go and

18:00have a look to see what we could do to improve this, if we could do anything. We

Transcript for Photo Engraving Slate and Granite (Cont…)

18:06can’t change the colour remember, the colour is whatever it is. The only thing

18:13that’s affecting this, let’s call it white here if we were looking for

18:17something that was white we can only possibly just crush the pixels up a

18:22little bit closer together because I do believe there are gaps in the

18:25Y-direction, we’ll go and look at that under the

18:28microscope. All right well, while that’s going on

18:34what I decided to do was to change the resolution from 150 up to 300 PPI this

18:44machine is not running at one hit per pulse it’s running at a very high speed all

18:51the time and it’s putting a large number of pulses down for every pixel. The

18:56question is how many pulses is it putting down for every pixel and the

19:01answer is when you do the quick calculation the whole background pulsing

19:05system is running at 20 kilohertz so that means that I’m going to get 11

19:11pulses per pixel at 300 dots per inch. The sensible thing to do would have been

19:17to have set the parameters for this particular picture to the same

19:21parameters that I had before and only change one of the parameters ie the dots

19:26per inch. That would have meant that I would have had twice as many dots in the

19:33y-axis and twice as many dots in the x-axis

19:40but hey I’ve decided to go a little bit overboard, ignore the rules slightly and

19:47I’m running at 40% power as opposed to 25% so I’ve got heavier pixels. So I’ve

19:54got more power going into each pixel, but I’m running faster so in fact I’ve got

20:00less power going in per pixel it’s a very strange balancing act that I’m

Transcript for Photo Engraving Slate and Granite (Cont…)

20:06trying to perform here and I’m second-guessing that I don’t compromise

20:10the clarity of the picture by blurring the pixels into each other. Now that

20:16didn’t seem to happen when I tried the same thing with anodized aluminium and

20:22we got up to a thousand pixels per inch. So let’s see what the results are. I have

20:30to say they’re looking pretty good so far.

20:36So stand here watching this picture and you’re so hypnotised by watching the

20:41picture you are not actually watching what the actual laser beam is doing. Look at

20:47that light, I mean that light tells us that we’ve got a huge amount of power

20:53going down instantaneously on pixel after pixel after pixel. That light

21:01doesn’t come for free from nowhere, that’s a huge amount of heat that’s

21:05being knocked out into every pixel and it’s quite phenomenal that this system

21:10can work that quickly. Now somebody’s going to ask me where did I get my

21:15Chinese slate from? Well the answer is from a cheap pound store.

21:24They would not be cheap and they wouldn’t be in a pound store unless they

21:28bought them in bulk from China.There’s no dust and there’s no fumes so it’s not

21:38there, we must be vaporising this material. Okay so the holes are very very

21:45small, there is a certain amount of 3D’ness on that picture. Perhaps it’s just

21:55my fingertips feeling holes and no holes but it’s pretty amazing isn’t it. Now I’m

22:03gonna try something a little bit different this time to see if I can

Transcript for Photo Engraving Slate and Granite (Cont…)

22:06enhance it, this is basically a wax-based floor polish. Now when I paint this onto

22:14wood it soaks in,

22:20and I can actually see that it’s changing color as it slightly soaks into


22:29Well I have to say that’s pretty impressive I never thought that I would

22:35get to 300 pixels per inch, 240 millimetres a second on a piece of slate

22:42and achieve a result like that. I thought it was going to be rather fuzzy and

22:46blurry and I think the secret really is all coming back to power management

22:52through this special mode. Breaking the pulses down into very small increments

22:58so we don’t do too much damage at a time but we do lots of damage over time with

23:04small increments. I think even from this distance you can see how much clearer

23:10and crisper black and white that one is as opposed to this one and it can only

23:16be the crispness of the blackness not the amount of whiteness because this is

23:22the same texture it’s the same colour as this, but it just looks crisper.

23:30I mean the whiskers on here are not bad at all, but my goodness they don’t half

23:35stand out much better on this one. Well I hope that’s an interesting session oh we

23:43could go on and we could do some black and white logos and some text but after

23:50pictures that’s kiddie stuff, this is the difficult stuff getting images down with

23:59the right sort of crispness and clarity. Understanding how we can do that, if you can

Transcript for Photo Engraving Slate and Granite (Cont…)

24:05understand how we can do that and you can second-guess what’s going to happen

24:08then hey you’ve got it cracked. Now I’m extremely pleased at what we’ve done

24:17here, I didn’t know what the results were going to be. I think you’ll agree that

24:22we’ve come to a very very satisfactory conclusion. Now I would like to get some

24:27more granite so that I can play around with some more polished black granite. Who

24:32knows what we could do with black granite, whether we get that up to 600

24:36dots per inch? But I think we’ve come a long way with photo engraving on various

24:40materials, over time we’ve covered card and wood,organic materials, now we’ve

24:45done mineral materials, we’ve done a little bit with glass when we did rotary

24:49engraving which is another mineral ish material but of course that was a

24:53completely different process. I was expecting this to be something similar

24:57to glass a sharding process, but it turns out not to be. This is much more of an

25:03evaporation process I do believe, but I think we’ll have a complete change of

25:08subject in the next session so until then cheerio.

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