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Anyone ever seen this effect before


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#1 rp88

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Posted 25 February 2016 - 03:25 PM

Ok, quick question to anyone who's ever burnt cd or dvd discs. Usually I use cd-rw discs, when one writes to them you can, afterwards, hold them up at an angle to the main light source in the room and you see that the middle of the disc is slightly different in colour to the outer part, the more data is on the disc the further out this division between colours is.


The images below display examples of this.
https://upload.wikimedia.org/wikipedia/en/4/40/DVD-4.5-scan_b.png
http://4.bp.blogspot.com/_f-VN9F37tV4/SY_bIigYgcI/AAAAAAAAAOQ/a-R74HrEKPM/s400/written+cd.jpg


The same applies when you burn dvd+r discs, though it's not quite so noticable.

It makes sense that this happends because a cd is potical media and by writing data to it you're chaning it's optical properties so it will appear somewhat different upon viewing.

But recently I burnt some files to cd-r. There was no noticable coout change at all. Anyone else noticed this? Why would cd-r discs not display the colour change that other types do?

Edited by rp88, 25 February 2016 - 03:25 PM.

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#2 Agouti

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Posted 25 February 2016 - 03:37 PM

But recently I burnt some files to cd-r. There was no noticable coout change at all. Anyone else noticed this? Why would cd-r discs not display the colour change that other types do?

How many MBs do these files add up to?  What brand CDs are these?



#3 NickAu

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Posted 25 February 2016 - 03:41 PM

Yes I have seen this before, If you look at any CD or DVD you can tell the difference between the burned ( written to ) and not burned areas.


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#4 66Batmobile

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Posted 25 February 2016 - 11:24 PM

I could be wrong, but if memory serves it's manufacturing differences between formats.

 

Long story short, for DVD-r/cd-r, the information is written to a dye layer on the disc from the center out.  For some reason, possibly because more data is written to a smaller section, on DVD-r's the color difference between the burned and unburned sections is generally much more pronounced than on cd-r's.

 

On CD-RW's, the info is written to a metal alloy layer, which may explain the more pronounced look there.

 

Actual commercially produced movie/music discs are a whole different story.


Edited by 66Batmobile, 25 February 2016 - 11:31 PM.

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#5 Agouti

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Posted 26 February 2016 - 05:31 PM

@rp88, was your issue solved?


Edited by Agouti, 26 February 2016 - 05:31 PM.


#6 rp88

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Posted 28 February 2016 - 12:59 PM

What I'm commenting on here isn't that one can see the burnt bits, one usually can, what I'm saying is I'm finding it strange that in this case I can't see the burnt bits on this particular disc type. The discs are the same brand, verbatim. There's no "issue" here, Just wondering whether anyone else has noticed that some types of disc (cd-r) don't seem to show a visible difference for burnt and unburnt regions whereas most othr disc types always have in my experience.

Post #4, that might explain it. A metallic layer on cd-rw discs would certainly account for the fact they have silvery and darker silvery colours (rather than shades of purpley iridescence on dvds), I can imagine how cd-r discs having rather less data per unit area than dvd discs would lead to a less significant colour change.

"Actual commercially produced movie/music discs are a whole different story"
They would all be full anyway, when one inserts one you always see it reading as having no free space.
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#7 Agouti

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Posted 28 February 2016 - 02:16 PM

Same questions:

 

How many MBs do these files add up to?  What brand CDs are these?






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