Smithsonian press release

Walter,
On Thu, 29 Sep 1994, homo obsolescensis wrote, quoting my posting:

>>I find it hard to make sense out of the second last paragraph. "At
>>higher values of temperature and relative humidity, they say, physical
>>damage is minimised" is either wrong, or just too subtle for me.

> The emphasis is on "physical". At lower RH many materials--gelatin
> films for example, as well as complex materials like paper--lose
> flexibility, at higher RH they are more flexible. Among the research
> that lies behind the CAL posting, for example, is Mecklenberg's work
> that charts the strain that develops in gelatin films at various RHs.
> This work was (I assume) done with paintings in mind, but think for a
> moment of a storage vault full of photographs...
> onward,
> w

Yes, you're right. I was ignoring the potential for physical damage at
low RH levels. But I still think the claim is confusing. While it is
true that low temps/RH prevent biological damage and minimise chem
reactions, and that higher RH levels (but *not* higher temp levels) do
contribute flexibility (but don't maintain flexibility), this is a
dilemma rather than a cause for relief. The tone of the press release is
"ah, we don't have to worry about these things any more", and this
paragraph can be easily read to mean "by providing conditions over the
range of 11 - 31 degrees and 35 - 65% we will enjoy the benefits of
minimal chemical reaction, minimal physical damage, and minimal
biological damage". If they mean that, I think they are wrong. And if
they don't mean that, it isn't a very helpful statement, because it
still leaves you with the dilemma of where to set the best level within
that range.

The way I would represent the situation you are referring to is to say
that we should recognise that the absolute limits we can accept are
temps and RH low enough to minimise chemical damage, high enough when it
is needed to provide flexibility, within the limits of long-term
elasticity of the material, and low enough to prevent biological damage.
These are the outside limits within which we must seek the appropriate
balance for the material we have and the outcomes we require.

So, I should withdraw the suggestion that they are wrong and just say
that if they are right, they are ambiguous.

Regards,
Colin

                                  ***
                  Conservation DistList Instance 8:23
                Distributed: Friday, September 30, 1994
                        Message Id: cdl-8-23-002
                                  ***