[Hallicrafters] S-120 receiver - celloluse nitrate lacquer?

[Richard Knoppow]

----- Original Message ----- 
From: "rbethman" <rbethman at comcast.net>
To: <hallicrafters at mailman.qth.net>
Sent: Monday, March 25, 2013 8:27 AM
Subject: Re: [Hallicrafters] S-120 receiver - celloluse 
nitrate lacquer?


> The old cellulose acetate was the base layer of old film. 
> It dates back to pre 1930's.
>
> The only nitrate on the old film was what was left of the 
> silver nitrate that was applied to capture the image.
>
> There are many films of that nature that are very 
> carefully stored, and are stored is small numbers in 
> chambers.
>
> I do have an S-120.  Most likely the "goop" under the 
> knobs is the brass that will seemingly appear from no 
> place whatsoever.  Every instance where I find this 
> happening is where the brass is in contact with leather.
>
> I have this happen to a number of older knives.  It isn't 
> hazardous, but simply a royal PIA to end up having to 
> clean.
>
> I don't know what mechanism is the cause.
>
> However, I have NO such happening to my S-120.
>
> Nitrate dope is still in use for aircraft doping of cloth 
> covered aircraft.  It causes that fabric to shrink taught. 
> It is the initial coat.
>
> Bob - N0DGN
    This is OT but the support used for most 35mm motion 
picture film unti 1951 was cellulose nitrate. Safety film, 
or cellulose acetate was used for 16mm film and no 16mm film 
was ever made on nitrate. However, the motion picture 
industry was reluctant to change to acetate because nitrate 
was supposedly less turbid plus the printing equipment was 
all designed to compensate for the shrinkage of nitrate. 
There were some very serious film fires due to nitrate. 
Nitrate supplies its own oxygen when burning so nitrate film 
fires are extremely difficult to extinguish.  Motion picture 
theaters were required to take extreme precautions to 
prevent film fires and to isolate them to the projection 
room if they occured.  Nitrate film base is inherently 
unstable but the degree of instability depends on the exact 
method by which its made.  It turns out that historically 
Kodak made the most stable base and Dupont the least stable. 
In 1951 the industry changed over completely to cellulose 
acetate.  However, acetate has a set of vices all its own. 
There have been at least three kinds of acetate material 
used as film base and it turns out that one of them 
"triacetate" was very unstable so much motion picture 
material made on it has been damaged.  See "vinegar 
syndrome" for more.
     The effects of the instability have to do with many 
factors and do not seem to have affected nitrocellulose 
paints.
     Also:  Silver nitrate is a component used in making 
photographic emulsions but there is little or no nitrate in 
the finished emulsion since it is converted to other silver 
compounds.  The developed film, provided its been washed 
properly, has only metallic silver embedded in a gelatin 
coating.  Color film has no silver, its bleached out in one 
of the last processing steps, leaving only dye embedded in 
the gelatin.
     Animal gelatin is still used as the basis for 
photographic emulsions since in 120 years nothing better has 
been found.  Some plastics are added in modern film but most 
of what is there is animal gelatin.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com