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I need to generate a guilloche border for certificate of authenticity (CoA) to be at the edge of the CoA. I'm talking here about the infinite curve that makes the certificate look "legit".

I'm planning on creating such a curve with a plotter with ball pen in it. That would ensure the curve is always a little bit unique (CoA will be scanned so that I can later approve it's a authentic certificate and misperfections in ball pen line will serve as a great generator of entropy, making it almost impossible to tamper with).

How to make such a curve? Possibly in Illustrator, but I don't really care which way.

EDIT2: Found out Illustrator has 'Scribble' filter. This is what I've done with it and kinda what I want to achieve, but in a more 'sophisticated' manner... sample

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errr... Excentro? –  Scott Aug 11 at 11:20
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The curve can not be infinite or your plotter would take infinite time to plot it. Howabout just using a watermarked paper. Besides its not the certificate paper that holds the secret ist the fact that it is being backed up by a phonecall to the original author. –  joojaa Aug 11 at 12:17
    
Yes, I was looking for exactly what Scott posted. Not sure if it is THE thing I need but at least we know how it's called. –  lmojzis Aug 11 at 19:08
    
@joojaa infinite as in letter "∞" is "infinite" –  lmojzis Aug 11 at 19:09
    
@Scott It is exactly what I'm talking about. Didn't know it's called Guilloché. Feel free to post it as an answer and I'll accept it. –  lmojzis Aug 11 at 19:13

2 Answers 2

Illustrator does not really excel at this sort of operation. This is why I linked to Excentro in the comment above. Excentro is specifically designed to create guillochés and it's artwork is exportable (as vector) to Illustrator. Of course, I realize Excentro is an extra cost.

The ways I can think to try and pull it off with only Illustrator include:

  • Pattern brushes
  • Transform Effects

With a Pattern Brush, you simply create tile-able base artwork:

enter image description here

Drag that to the Brushes Panel and choose Pattern Brush for the first pop-up window.

The second window will allow you to set some auto-generated corners (Illustrator CC or newer only):

enter image description here

You can try a few of the auto-corner options while the dialog is open to see if any fit well. If not, you may need to generate a custom corner. Unfortunately, custom corner creation is much more intricate and dependent upon the actual artwork. So, I won't go into custom pattern brush corner creation here, but there are tutorials on the web.

After clicking OK in the brush dialog you can simply draw a shape and apply the brush to it.

enter image description here

The more intricate and detailed the original brush artwork is the more extensive the overall final appearance can be.

Effects which create smooth curves really come down to Stylize > Scribble and Distort & Transform > Zig Zag. Neither of these on their own does, what I would consider a good job:

enter image description here

Zig-Zag would require rounded corners to work if no manual alteration is desired. But ultimately it's just one path and not what I would consider a guilloché. You'd have to double-up objects and carefully configure things to get any sort of guilloché aspect.

Lastly you could combine an effect with a pattern brush:

So I start with simple base art and apply an effect to create a guilloché-like circle:

enter image description here

I then apply another effect (saying OK to the warning that pops up) to move and copy this object horizontally.

enter image description here

Then I draw a rectangle with no fill and no stroke and move it behind all other artwork. The rectangle "splits" the first and last circle in half. This ensures repeating brush patterns will repeat at that "half circle" or "half emblem", thus lining up the area of repeat.

enter image description here

I then drag that artwork to the Brush Panel and choose Pattern Brush when asked. I set the auto-corner option to Auto-Slice and click OK.

Then simply draw a rectangle and click the brush I just created:

enter image description here
My pattern-defining rectangle is slightly off on one end. This is resulting in a small overlap where the repeat happens. Easily corrected, but I closed the file (without saving it) before I noticed the repeat issue.

Is this technically a intertwining guilloché? No, but it does look like it. Depending upon your original base art, you can create some very nice, intricate, appearing brushes in this way.

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Create a Security Seal in Illustrator Using Guilloche Patterns

This comprehensive tutorial will help you with all your Guilloche pattern needs! I was just researching on my own and found this post and this link. Figured I might as well respond with what I had found in my search.

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