Session 28 – Photo Replication with Other Materials

The Concise RDWorks Learning Lab Series

Welcome to Module 3 of the new Concise RDWorks Learning Lab Series with Russ Sadler. Module 3 will build on the information learned in the previous modules and will be targeted on the differing types of laser engraving methods and the techniques needed to consistently achieve great engraving results. So lets learn some great new Laser Photo Engraving Tips.

In this Session, Russ continues the Photo Replication theme and explains how to great results on non-organic materials. This time it’s the turn of anodised aluminium, and Russ teaches us the particular characteristics of this material for laser engraving. Using his proven Photo Replication theme of “One Pixel equals one dot” he prints a superb rendition of the fox at 254DPI onto white anodised aluminium.

Release Date: 21st January 2022

Over the last 6 years, Russ has built up a formidable YouTube following for his RDWorks Learning Lab series which currently has over 200 videos.

The original RDWorks Learning Lab series on his “Sarbar Multimedia” YouTube Channel, follows Russ as he tries to make sense of his new Chinese laser machine and to sort out the truths, half truths and outright misleading information that is available on the web.

Six years later with over 3 million YouTube Views under his belt, Russ has become the go to resource for everything related to the Chinese CO2 laser machine user or wannabe user.

Laser Photo Engraving Tips: High resolution laser engraved fox image
Laser Photo Engraving Tips: High resolution laser engraved fox image

In this new series, Russ has condensed his knowledge and experience of the last 6 years to provide valuable information and insights into the purchasing, understanding, use, repair and maintenance of the Chinese CO2 laser machines and their key component parts.

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Session 28 – Photo Replication with Other Materials

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Session 28 – Laser Photo Engraving Tips – Photo Replication with Other Materials

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Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials

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The Concise RDWorks learning lab with Russ Sadler.

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Session 28. Photo replication with other materials.

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Well, today we’re going to talk about photo replication on other materials.

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What we’ve seen so far are basically organic materials.

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The problem with paper, card and wood is their sensitivity, the damage threshold.

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Here, we’ve got a picture of the laser beam itself now, whether it’s before the lens or after the lens.

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It is essentially the same. The laser beam has a very high intensity central part to it.

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And as we move away from the centre of the beam, the intensity, and that’s the most important word you must remember, starts dropping off look very

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considerably until we get to this red zone where we’ve got hardly any intensity at all.

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And basically, what that means is we can do damage with intensity.

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The more intense the beam, the faster we should do damage, so as we get to the blue zone,

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we’ll still be able to do damage because there is still intensity there.

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But remember this term exposure time, because there’s less intensity, we need more exposure

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time to do damage and even more exposure time to do damage down here,

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with such low intensity. Organic materials are particularly sensitive to this

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variable exposure problem because we have got different intensity across the beam.

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Now here’s a hole that we burnt in some card. This was a dot,

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remember. It’s only, well, roughly about 0.1 diameter that dot, although this was a fixed period of time for this dot.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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The time was not sufficient here to allow the intensity to burn through the paper, and here it was even less intense.

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So it did even less damage in the same time that the central part of the beam was able to burn a hole right through the paper.

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So here we’ve got very typically those three zones that you’ve seen on the previous image.

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So consequently, you can see the three zones of intensity when you start using organic materials.

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Now we’ve spent a lot of time talking about the laser process itself.

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Almost 50 percent of understanding about lasers involves understanding about materials.

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Now, in the last session, we were dealing with organic materials, wood paper card.

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But this material here, aluminum has got a completely different way of reacting with the laser beam.

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First of all, it’s a metal. And I’ve already explained to you what happens to metals,

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you fire a laser beam at this piece of aluminum and 99 per cent of it will bounce back at you.

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It’ll bounce back and it could damage the lens. So you don’t fire the laser beam directly at aluminium.

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But we can engrave aluminium. How and why?

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A process that can be used to change the surface of aluminium is a process called anodizing.

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And basically, what they do is it takes the raw aluminium and in a in a process of electrolysis, electricity and a chemical.

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The surface of the aluminium changes from raw aluminium into something called aluminium oxide, now aluminium oxide,

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you will be familiar with, I’m sure. It’s the white, grainy material that’s used in grinding wheels very, very hard material.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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It’s also used in things like sandpaper or Emery paper. So it is a very hard material, but it is not a metal.

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So we’re converting this metal into a non metal, which means when we fire the laser beam at it now, it will absorb the energy.

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Now there are several different types of anodising. One of them could be to just put a very thin layer of oxide on the surface of the material.

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Most of the processes involve this buildup of a cellular structure onto the surface of the aluminum.

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As you can see here, we’ve sacrificed some of the aluminum and we’re building up these.

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These look like combs, but they’re not.

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They’re actually very small hexagonal pores that sit on the surface of the aluminum like a honeycomb structure.

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And this can be several microns, 20~30 microns thick, you know, over the thickness of a hair, which doesn’t sound a lot,

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but actually because this is a very, very hard material, it has amazing wear resistant properties.

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So if you’re familiar with anodising, you will say, well, hang on this there’s red anodising, yellow anodising, green

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anodising, blue anodising, silver anodising, gold anodising where do all these colours come from?

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Well, they don’t come from anywhere. What happens is this is the first part of the process creating this aluminium oxide honeycomb system.

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And then at one stage, in the process, they dip the product into water based dye, which tends to hang into the bottom of these little cells.

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And that is where the colour, the various colours come from to produce all these wonderful coloured anodized aluminium.

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And finally, there is a process after this colouring process which seals these pores off.

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How does this affect us when we try to engrave it? When we fire the laser beam at it?

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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Remember I said to you when we were speaking earlier about the low damage threshold of wood and organic materials.

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Well, this stuff requires something like over 2000 degrees C to make it melt.

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Not only is it a very high damage threshold, it doesn’t absorb the energy rapidly.

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It requires a long ish time to heat this up to over 2000 degrees C to damage it.

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In the meantime, they’ve only got to go up to two or three hundred degrees C, and this stuff will evaporate off.

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If you make this disappear. The colour what you’re left with is this stuff, which is a white crystalline structure, regardless of what the colouring is.

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It will always be white underneath.

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You will just see the high intensity part of the beam evaporating the dye, and it will produce just a small, clean white area.

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There will be no shading to the white area because of this here.

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The dye is either there or it isn’t there. There’s nothing in between.

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Unlike an organic material where you’ve got these various shades of brown because

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we’ve got different types of damage taking place because of the different intensities,

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aluminium falls into this category that I like to call a binary colour.

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It’s either the dye colour or the white background colour, that’s it, there’s nothing in between and that makes it great for photo engraving.

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Here’s a piece of black anodized aluminum. As you can see,

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I’ve just been playing with a little bit of Matrix test on here to try and demonstrate to you that you can’t really get colours other than black and white.

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We’ve managed to get ourselves a bit of a gray along here, but in essence,

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I’ve only put such low power in there that I’ve only partially evaporated some of the black dye. In general,

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you’ll get all white. So I really wouldn’t try and do anything like grayscale engraving with this because it isn’t going to work.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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We know that this lens here is capable of producing 0.1 dots.

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So what we’re going to do, we’re going to try and get some nice, the sharpest dots we can get with that lens.

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And that will mean changing the focus because the focus that we had for wood will not be suitable for this.

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We’ve got the power and the speed set to 400mm a second and fourteen point five percent power the same as we had when we were doing the foxy picture.

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Now that looks quite severe, to be honest.

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Can it be better by changing the focus? So at the moment, we’re at about eleven point two.

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If I go down by, say, half a mill to ten point seven. Eleven point two, let’s go up to eleven point seven.

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I’m also going to do a similar set underneath here below each one.

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I’m going to reduce the power to 12 percent. OK, now anodised, aluminium is one of the best materials for producing dots.

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This white aluminum oxide doesn’t start boiling or disappearing until probably something over 2000 degrees C.

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Whereas the dye in the foreground? It’s a water based solution with some colour in it,

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so certainly no more than 200 degrees C and this white will appear because the black has been evaporated.

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So that’s the mechanism by which we’re producing these white dots. Because of that huge temperature difference.

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We haven’t got this three phase variation of power around the outside of the dot.

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The other thing I want to talk about here is something we discussed in the previous session about making dots and

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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how making dots with a glass tube machine relies very much on the response time of the high voltage power supply.

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Now these look like very nice dots. These are done at eleven point two Focus point with a power of 12 percent and a speed of 400mm a second.

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As I demonstrated, when we were using the HV Power Supply, I only showed you the example of a 100mm a second and changing the power,

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to change the size of the DOT.

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Well, if you keep the power constant and change the speed, you can achieve much the same sort of thing you can control the size of the DOT.

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But, let’s look at the central row of dots.

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There’s the top row of dots and dashes, which don’t seem very consistent, but where are the middle row of dots?

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They aren’t there! Exactly the same focus, but the power has now been increased from 12 to 14 and a half percent.

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Look at the size of the dots now. They’re much, much bigger.

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But. We’ve now got our central row of dots back.

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Okay, now I’m going to talk about that top row of dots in a second, you’ll see that these dots are actually smaller than these dots.

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Well, if you look at the spacing between these dots, there is a different timing effect within the high voltage power supply.

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The power is dropping off completely, and then it starts from square one again and comes up and produces just a small dot,

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drops off completely, comes up and makes just a small dot, whereas here we’ve got dots spaced much closer together.

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Here we’ve got a three pixel gap one Pixel one two three one Pixel, one two three, and here we’ve got one Pixel one Pixel one pixel.

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So the gap between these pixels, or the time between these pixels is a lot less.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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And so consequently, what happens is the power is on and then it starts to drop off, but it doesn’t drop to zero.

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And before it gets to zero, it says I want some more power.

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So it comes back on at a much higher power level than it would do if we allowed enough time for the power to drop off completely.

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Do you understand what I mean about the timing issue and the response time within the power supply?

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How it can affect the size of your dots? This is a very, very important aspect of the machine if you can understand how this works.

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You’ll understand a huge amount about your machine.

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Remember, I raised the focus up to eleven point seven, which was there, and now we’ve got some rather strange set of dots.

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Then we went half a millimeter low at ten point seven, which is what this is.

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And yeah, the dots are a bit on the messy side.

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You see, we’ve got very, very small dots there and large dots at the top because there is no time between these dots.

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I know they might look like dots to you, but they’re not dots. What’s actually happening is this is the stepper motor that you’re seeing here.

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It’s going step. Then it’s going quickly, step quickly, step quickly, step like this.

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So every time it steps, it stops for a few microseconds and allows a bigger burn.

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Then it jumps and allows a bigger burn. The signal for that pixel starts there and it’s on continuously till it gets to here.

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So we should have a continuous line, not a series of dots.

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That was a mistake that I made very early on. So it wasn’t until later on that I realized that these are not bitmap dots.

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These are actually stepper motor dots. .

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So we’ve loaded our little fox image in, and I had to go back to Photoshop and I’ve had to resize it to suit my piece of material that I’ve got.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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It’s still two hundred and fifty four pixels per inch. So because I’ve made it smaller.

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Remember what I said? I put slightly less pixels in each one of these details.

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Although the resolution of the picture remains the same, the quality of the picture has been slightly degraded because I’ve made it smaller.

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What you must remember, is this most important! Up to now, we’ve been producing black dots or brown dots on white paper or light material.

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Now we’re going to produce white dots on black material, so I’ve got to go into the parameters now.

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And one of the features in the parameters is this one here, which is negative engrave.

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So I’ve got to swap this round and I’ve got the parameters set correctly for 13 percent and 300mm a second.

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OK, now I can have a quick look to see what the preview looks like?

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And there is you see the preview comes out the right way round. So remember, we start the program off and we put it onto pause mode.

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Start, pause. The program is now loaded, I can let it go.

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We will come back and look at that later. A photo replication, no modification to the picture at all.

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I’ve got the settings slightly wrong, I need a little bit more power.

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Because I haven’t taken quite enough black out of these dark areas,

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so I could do with a little teeny weeny bit more power to pull the whiteness out a bit more.

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Hey, it’s not a bad image for a starting point. I’d like you to take a look at those two images.

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There’s a very subtle difference between them. This one was done at 13 per cent power and this one was done at 14 per cent power.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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Now remember I said to you, we could really do with a little bit more power in there to make it whiter because remember,

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we’re leaving black behind and we’re actually burning white dots.

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We put a little bit more burning power into the white and you can see the nostrils in the nose now,

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whereas you can’t see the nostrils in the nose there. And look how much brighter and clearer the eyes are very subtle differences.

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But if you understand what you’re doing,

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and that’s the whole point of this exercise to teach you the importance of dots and the power of dots, you’ve got black dots.

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If you’re using organic material. You’ve got white dots,

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in other instances, if you’re engraving on to black. We’ll now go on to a slightly different sort of material.

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And here we’re doing something completely different. We’re producing white acrylic from black acrylic.

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We’re putting white dots on black acrylic. That’s interesting, how is that possible Iwonder?

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And apart from this strange mark, something in the material down here, that’s not bad.

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The eyes are good. The nose is pretty good.

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Some of the whiskers have disappeared because of the texture of the material in the background.

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It’s certainly not as good as anodized aluminum, but hey!

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It shows you what you can do if you understand the material. Now I will show you how and why that material turns white. As you keep finding out.

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This laser subject is laced with science. Whichever way you turn.

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And although I’m not going to go into the theory of colour, it is a fascinating part of the colour theory.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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What I’m just about to show you. At the moment, the light is passing right through this jar of water and the glass as well.

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The only time that the light is being stopped is when it hits my hand and the light is reflecting off my hand so that you could see my hand.

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So when my hand is not there, the light carries on passing through until something else.

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But if I do this? What colour is it now?

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Yeah, it’s white. You can’t see my hand through it.

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And that’s because there’s millions of bubbles in there which are now intercepting the light before it hits my hand.

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And you are seeing light being reflected off of those bubbles.

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So bubbles or solid particles in air like steam.

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Turn white, because they are reflecting the light. Now that’s basically the theory behind what you’re seeing there.

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This is shiny black acrylic, which has somehow turned white.

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Black acrylic doesn’t turn white,

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but you have to understand the properties of acrylic so that you can set the power just right to give you this effect.

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This is looking at some pixels, and we’ve got single pixels and double pixels here and under the microscope at 50 times magnification.

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And you can see relative to the background, they look white.

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If I change the magnification to say 400, there’s a pixel.

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Let’s just run across to the next pixel. And what do you see?

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Bubbles. Bubbles and bubbles. Look at them everywhere you look.

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Bubbles. And that’s what catching the light and creating the white effect on black acrylic.

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If you burn it too much, you will melt and evaporate the material.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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This material melts at 160 degrees C and it stays liquid until 200 degrees C,

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where it evaporates just like steam and disappears into the air as small particles of acrylic and you can re-condense those back to solid acrylic.

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And that’s the white crap that finishes up on the surface of your material.

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If you are not careful about it, but if you catch this just right,

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you can leave a pool of liquid in your dot that will freeze just after it’s beginning to boil.

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So a certain part at the center there will be a little bit deeper because it started to evaporate.

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But this is boiling acrylic, which is then just frozen, and that’s what’s causing the white effect.

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And now we’re in grading on slate. The image on there,

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although it looks white, it’s actually grey.

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And again, we’ll take a look at that under the microscope because this is a completely different method of marking the surface.

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Now there’s a whisker that’s unaffected.

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OK, but beside the whisker, we’ve got pixels, and let’s see if we can pick up a single pixel somewhere, should we?

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Well, somewhere like’ somewhere like these, these are all single pixels.

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So let’s go in and have a look to see if we can see what’s actually going on.

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So we change from 50 magnification to 400 magnification.

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And again. If you look carefully, as I zoom in and out past some of these pixels, can you see bubbles again?

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Look. And wherever we look, we shall begin to see.

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Bubbles. Because what are we doing here,

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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this is a sandy type of material originally. It was silt in the bottom of the ocean.

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A silicate. And what’s happened now when we heat it up, it’s turned into gray glass.

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You can see the reflections here off the glass, of the surface of the glass.

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If I was to put lots of power into this, I will actually create bubbles of glass out of slate.

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So Slate is not the same as acrylic. Yes, it does produce bubbles, but those bubbles just happen to be in the glass.

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These are pieces of glass, melted globs of glass on the surface, grey glass.

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And that’s what you’re seeing when you engrave slate.

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If you want to make coasters from it, it’s dishwasher proof because you can’t wash the glass off. That’s engraving on glass.

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Not very interesting, really, is it?

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Until you’ve got a black background behind it, two types of engraving on glass, and I can feel this one is what I call sharded.

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It’s like little stone chips on your windscreen. We’ll, look at that under the microscope as well.

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There’s pixels engraved into glass.

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There should be some sort of scan lines across here where it would be obvious that you’ve got scanning taking place.

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These are all rather random, different sizes, different shapes.

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And that’s because, as I said, each one of those is a random stone chip caused by rapid expansion of the glass when

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it gets heated and it just pops out because the surrounding area hasn’t expanded.

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So those are thousands of little stone chips. Let’s just have a look at that at 400 times magnification.

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But the randomness of the shape tells you that these are not melt blocks because if they will melt blobs.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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Even though they’ve got round edges, I think these are shards when you feel the surface of the material.

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You can feel it’s not melted.

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It’s definitely rough, and if you put your fingers over the surface,

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you may well pick up some little shards of glass in your fingers, so be very, very careful.

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I mean, you can see the crack boundaries there, can you? Look at the way the light is catching you there.

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I mean, you wouldn’t get that from a round blob.

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So that little clue there with all those lights in it shows you that we’ve got a little fracture surfaces there.

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So we take a look at these materials under the microscope so that you can see all the different ways in which material can be damaged.

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They all look roughly the same. These are all what I call binary materials.

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There’s only one colour that you can produce with. There are no shades of white.

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When you engrave glass, there’s no shades of grey.

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When you engrave slate, they’re whatever colour the material comes out, two different slates from different parts of the world engraved differently.

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Chinese slate is actually very good. It comes out fairly grey, light grey.

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You get stuff from somewhere like Spain or other places in the world.

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It comes out brown mud color because this basically is compressed mud.

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It’s silt. It’s been compressed over millions of years before it’s been mined out as slate.

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Good job is not a pair of jeans I want to wear. Yeah, I’m far too fat for these now, just to give you an idea of what’s possible.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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So I think probably I could have gone a little bit less on the power there because look, you can see that I’ve just slightly burnt the material.

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It was it was an off the wall experiment, that I thought you might be interested in.

Transcript for Laser Photo Engraving Tips – Photo Replication with Other Materials (Cont…)

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Last updated August 26, 2021

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