UV reactive patch on 1991 $20 Bonin-Thiessen

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I've got something bizzare that i'm hoping somebody can shed some light on.  I recently purchased a minty 91 $20 Bonin-Thiessen AWB prefix in Perfect UNC condition off ebay and was overlooking it with my UV flashlight.  On the back of the note there is a square patch that measures about 1.7x1.7cm and glows white in reaction to the UV lamp.  The patch seems to glow brighter on the part that the foil security patch is present.  When exposed to UV on the front the patch is not visible.  Now i'm a novice collector and this may be common, but im curious if it was something that was added later or some new security feature I was not aware of at the time.  I searched high and low to find out more but to no avail.  I scanned the note and over layed the front of the note in reverse to simulate what im seeing.

{http://www.dmt07.com/gen_img/CAN20_BACK-1991_UV.jpg}

Thanks!

I've seen this before on Birds $20s and all Journey notes except for the 2002 $5s.

The colour seems to be more of a yellow or orange though, and is often quite faint. Only a good UV light will pick it up.

I do not know what this square is for. It could be a security feature, or possibly some sort of identifier that enables or makes machine processing more efficient. You could try asking the Bank of Canada, but if it is a security feature of any sort, I doubt they'll say a word on it.

Hmm interesting, well that's certainly a thought.  I'll have to dig around some more, though i'm sure with the resources on CPM somebody will know the true answer behind this.

I've got something bizzare that i'm hoping somebody can shed some light on.  I recently purchased a minty 91 $20 Bonin-Thiessen AWB prefix in Perfect UNC condition off ebay and was overlooking it with my UV flashlight.  On the back of the note there is a square patch that measures about 1.7x1.7cm and glows white in reaction to the UV lamp.  The patch seems to glow brighter on the part that the foil security patch is present.  When exposed to UV on the front the patch is not visible.  Now i'm a novice collector and this may be common, but im curious if it was something that was added later or some new security feature I was not aware of at the time.  I searched high and low to find out more but to no avail.  I scanned the note and over layed the front of the note in reverse to simulate what im seeing.

{http://www.dmt07.com/gen_img/CAN20_BACK-1991_UV.jpg}

Thanks!

From what I understand, this was a security thing "unpublished", just like the veteran's blazer on the journey 10 (try it).  Not sure when it is added, but I assume at some point after paper creating, and during printing, seeing as how it would be made to appear only on one side.  I simply do not know for sure.

I looked through the notes I have and found that the changeover to this "fluorescent square" occured somewhere between AVA (without square) and AVZ (with square).  The CBN printed notes have also this square, and begins between ESL (w/o) and ESZ (with)  prefixes.  I also looked the other notes and found that no birds 5s and 10s have this fluorescence.  But the 50s got this feature between the prefixes FHC (w/o) and FHS (with), and for the 100s:  BJB (w/o) and BJH (with).

Here a photo of this square.  I took it through a yellow filter to block the excess of the blue light reflected by the paper to the camera without blocking the yellowish fluorescence.  Otherwise, the square is drown under the blue light reflected by the note and is invisible (the CCD is more sensible to the blue light than our eyes...)

{http://img256.imageshack.us/img256/5428/20birdsfluo.jpg:http://img256.imageshack.us/img256/5428/20birdsfluo.th.jpg}

Wow great find there copperpete!! Strange that they would let this 'security' feature slip by as it would have seemed purposeful to inform the public about its usefullness in counterfeit detection you'd think.  I also noticed the square isnt in the same place by the looks of it according to your attached picture.  Does the square float around in different positions depending on the denomination?  Or does the placement seem somewhat random?

In all notes I looked to, this square is much in the same place, regardless the denomination.  But there is a slight variation in the position, which is normal during the printing process.

It would be great if some members can take a look to their notes to find the exact changeover prefixes (even to find out if it occured in a given prefix)...

Incidentally, I remember that I posted some years ago (at least three years ago...) and I posted a picture of this square on a 10$ bill.  Mabe someone can find this old post?

I finally found this old topic about this fluorescent square, posted almost exactly four years ago...

http://www.cdnpapermoney.com/forum/index.php?topic=1934.msg10870#msg10870

Unfortunately, the images are missing...

Courtesy of a friend of mine, here is another photo of the security square under regular light but viewed obliquely.

{http://img256.imageshack.us/img256/869/securitysquarer.jpg:http://img256.imageshack.us/img256/869/securitysquarer.th.jpg}

Still no authoritative knowledge on the true function or purpose of this device.