Hi, Tom,

You raise a good question. I qualified my statement in that I was 
concerned with hydrolysis but there is another factor.

I understand your point about acetate tapes and I had to hydrate a 
65-year-old carbonyl iron tape when I transferred the Mullin-Palmer 
collection, but...

If you research at the Image Permanence Institute at Rochester Institute 
of Technology, you will find an application called a "Preservation 
Calculator" and they use the relationship between room temperature and 
relative humidity to estimate the number of years before some amount of 
decay sets in. I don't recall all of the details, but I suspect there is 
a paper explaining the calculations somewhere on their website.

Here are a few examples
Temp °C / °F -- RH -- Preservation Index (Years)
    20/68 -- 40 -- 58
    20/68 -- 50 -- 44
    20/68 -- 60 -- 34
    22/72 -- 40 -- 45
    22/72 -- 50 -- 34
    22/72 -- 60 -- 26

As I understand this, it applies generally to all organic-based 
material, and I think cellulose acetate falls into that category.

At none of these combinations, is there a risk of mold germination, but, 
for example
    25/77 -- 70 -- 14
The program estimates 156 days until mold germination.

I know in growing up in a non-air-conditioned house in Forest Hills, New 
York, our basement had mildew and perhaps mold. Here with central air 
conditioning and a dehumidifer in the basement, I do not detect any 
mold/mildew and the numbers don't generally go above 50%.

One thing that still bothers me to some extent is when one thinks of 
what %RH is a measure of, the amount of water vapour in the air relative 
to its saturation point, the less I am convinced that this is truly the 
correct measure. %RH varies with temperature for the same moisture 
content. Dew Point is another interesting way of looking at this and IPI 
also has another version of the Preservation Calculator called a Dew 
Point Calculator.

Cheers,

Richard


On 2011-02-09 7:17 AM, Tom Fine wrote:
> Hi Richard:
>
> 40% for acetate and early polyester too? I thought low humidity only 
> for known sticky-shed formulations??
>
> My experience with early-era brown-oxide tapes is that they curl/warp 
> less and get brittle less if kept at more typical Northeastern US 
> humidity levels. Tapes I've handled that were kept in very dry 
> environments were sometimes very brittle and in extreme cases would 
> shed oxide as they moved thru a transport. Splices also tend to dry 
> out and fail at low humidity for these era tapes.
>
> -- Tom Fine
>
> ----- Original Message ----- From: "Richard L. Hess" 
> <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, February 09, 2011 7:10 AM
> Subject: Re: [ARSCLIST] static noise
>
>
>> Shai,
>>
>> Thank you for passing this along. Sadly, the author, John Pytlak, 
>> passed a few years ago, as you may recall. He was one of the real 
>> bright lights on the AMIA list. Several others are also gone.
>>
>> I would caution about handling magnetic tape long-term at 50-60 % RH 
>> as it might increase hydrolysis. The general recommendation for tape 
>> is 40%.
>>
>> Regards,
>>
>> Richard
>>
>> On 2011-02-09 5:55 AM, Shai Drori wrote:
>>> Dear members
>>> I received the following link through the AMIA list. I was about 
>>> vitalizing film but turns out Kodak has a few suggestions about 
>>> controlling static build up. Worth reading.
>>> Shai
>>> static 
>>> <http://www.kodak.com/US/plugins/acrobat/en/motion/newsletters/archived/pytlak/booth.pdf>
>>>
>>
>> -- 
>> Richard L. Hess                   email: [log in to unmask]
>> Aurora, Ontario, Canada           (905) 713 6733     1-877-TAPE-FIX
>> http://www.richardhess.com/tape/contact.htm
>> Quality tape transfers -- even from hard-to-play tapes.
>>
>

-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada           (905) 713 6733     1-877-TAPE-FIX
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.