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Excellent question.   Why not photo-admittance?  Well, they don't  
call it that, but they do use it, too...
Wiki has a page on CD glass mastering and explains that there are two  
kinds of photoresist (positive or negative) that can be washed away,  
after laser developing, but there is also
NPR (non-photoresist) glass mastering, which uses an organic polymer  
dye as the laser-beam target layer.   This dye layer is deeper than a  
pit, much the same as the lacquer layer, on a blank destined for  
vertical or stereo cutting, is deeper than the most deep, intentional  
embossing (gouge?).   The pitch on a CompuDisk or Zuma is set to  
avoid hitting the bedrock of the supporting layer, whereas I believe  
that the photoresist layer,  in the former-mentioned CD glass  
mastering method, is washed away clean down to the substrate - unlike  
a well-cut lacquer.   Fortunately, the CD player is only trying to  
make a variable strobe light display, rather than musical wiggles...  
at that point in the chain.


Andrew






On Jan 23, 2011, at 7:49 AM, George Brock-Nannestad wrote:

> From: Patent Tactics, George Brock-Nannestad
>
>
> ----- are they not etched into the glass afterwards? What is the  
> photoresist
> resistant against?
>
> George
>
>
>> Regarding CDs, the pits are in a thin photoresist layer that is  
>> spun onto
>> the glass substrate.
>>
>> Jerry
>> Media Sciences, Inc.
>>
>>> -----Original Message-----
>>> From: Association for Recorded Sound Discussion List
>>> [mailto:[log in to unmask]] On Behalf Of George Brock- 
>>> Nannestad
>>> Sent: Saturday, January 22, 2011 6:09 PM
>>> To: [log in to unmask]
>>> Subject: Re: [ARSCLIST] How many 78s to the Matrix
>>>
>>> From: Patent Tactics, George Brock-Nannestad
>>>
>>>
>>> Hello,
>>>
>>> Stewart Goodeman wrote [quote]:
>>>
>>>  I know in 1943, when they recorded the Rodgers and Hart
>>>> revival of "A Connecticut Yankee" they actually used glass.
>>>>
>>>
>>> ----- just to avert any confusion: glass means that the disc that
>>> supported
>>> the layer that the cut was made in was made of glass. The layer  
>>> could
>> have
>>> been lacquer, or it could have been wax, both were used. It has been
>>> thought
>>> that glass was a cheap substitute for aluminum that was the most  
>>> used
>>> material for lacquer mastering discs, due to other uses for aluminum
>>> during
>>> the war. But in fact, the quality of the cut in glass-based discs  
>>> was
>>> better
>>> than for aluminum, because the surface of glass was much smoother.
>>>
>>> This is very different from the use of glass in the manufacture  
>>> of CDs;
>>> here
>>> the pits are really represented in the glass as a stage of  
>>> manufacture.
>>>
>>> Kind regards,
>>>
>>>
>>> George