Magic Ink to temporarily dye a bright surface ?

As a child we all have used "magic ink" to fool our friends. It leaves a dark blue spot on any surface and after a while it disappears on it's own.

What if we dye our light colored plywood with it to allow our laserbeams a better absorption? It disappears under contact with CO₂, which we produce plenty while engraving/cutting.
Maybe we'd have to bath our laser bed in nitrogen to prevent early contact with natural CO₂.
It would be perfect, if we could let it dry in nitrogen gas while it keeps it's dark color. Wet plywood is not the best to engrave, I guess.

I found a receipt how to make this ink ( in german ).

If you know of any other method to dye plywood and let it disappear afterwards, you're welcome.
-Olaf

Edited 1 time(s). Last edit at 01/15/2016 07:10AM by o_lampe.

Hi Olaf,

I'm engraving and cutting plywood with the 445nm laserdiodes - engraving (or the first pass) carbonize the surface, so it's dark brown and will absorb the next passes too.

The problem is the narrow V-shape of the cut - the next passes will be caught/absorbed by the walls, so only a fraction of the power will be left for cutting in depth

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Viktor
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I've read in LPF forum, the three element glass lens has a better beam shape for cutting than the expensive G2 lens? What's your experience?

... I'm using the standard collimating lenses, which are inserted into the housings at lasertack - could be this part:
[lasertack.com]

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Back in the day I experimented a lot with all sorts of laser diodes and modules.
From there I can tell the right lens for a diode assemble really makes all the difference in terms of quality.
I needed superior beam qualities to test hologram making with simple laser diodes instead of gas lasers.
A single lens on most diodes will give you very small focus point - good enough for most things but if you check the beam outside the focus area it appears "dirty" and often in weird shapes.
It also means the usable depth of the beam is quite limited unless the diode produces a wide beam so you can use a long focus.
On the other hand 3- or 5-lens systems first prepare the beam to be as even as possible so the last lens(es) like a beam expander, then the beam is focus from that.
As the result you get an adjustable focus point that does not change the quality too much, in return that means the usable depth of a cutting beam is much deeper.

IMHO and based on my experience with holographic setups I would say a single lens loses at least 20% of usable power to beam scattering and lack of focus quality.
Also if the lenses are not optimised for the wavelength in use you will lose power again as the material absorbs some light.
A coating on the lens is only good for photographic setups or colored lasers powered by IR to filter out the dangerous and invisible light.

In many cases the actual optics of a laser cost much more than the diode powering the system

I am surprised you have issues engraving the ply. I too have had issues, but I thought it was related to the fact that the laser I am using is a measly 300mW (or thereabouts... red DVD burner).
With my red laser, trying to engrave ply would sometimes work and sometimes would not. Once the burning started, it seemed to keep going, but it wouldn't always start. The lighter the ply, the more problematic it was. I tinkered around with it for a bit and this is what I have found:

I first started by laying black paper down on the ply. It worked where the paper was touching the ply, but this was very hard to control. Especially as the edges of the paper would curl up off the ply as they burned.
Then I tried sticking down masking tape and colouring it black. This worked better, but it smelt bad (not sure if it was the black ink, the tape, the glue, or what), I would often go over the edge with the black texta and mark the ply, ruining it..., and the tape would leave a sticky residue.
Then I tried sticking down the blue painter's tape I had for the bed of my 3d printer. It wasn't too bad; no black texta issues, I don't think it smelt as bad, and I can't remember if there was a sticky residue. But the engraving wasn't overly deep (it's pretty thick tape).
Then I came across a thin black masking tape called washi tape. It's great! burns through well, no sticky residue, no offensive smells. I often use it now when I engrave (which isn't too often). The only problem is that all I can find are small rolls 15mm width, so it can be tedious. It would be nice to have it in wider rolls.

I have done some other experimenting, more along the lines of the 'magic ink'. We occasionally buy Crayola Washable Poster Paint for the kids because it washes off most things well. I tried smearing this on the ply before engraving and found it works as good as anything I have tried. It washes off afterward well too. I used the blue because of the blue, red, yellow and white I had, blue was the best bet for a red laser. I found only a light smearing was enough to get good results, and that if I smeared it on a bit heavy, some would remain in the grain when I washed it off. This is not good. It wasn't much at all, but even a small amount is noticeable when it's blue. I think if I tried with black paint, any that remained in the grain would not be noticeable as anything other than the grain itself. Unfortunately the nearby toy shop that has black requires me to by a dozen pack of paint to get it, and it isn't cheap, and it isn't the exact same stuff, so I have yet to try it. One day I'll get around to it.

Anyway,
Now you know my secrets!
Hope this helps... or at least is somewhat interesting.

Eric.