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,
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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.
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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.
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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…)
