Re: Positive Test for Platinotype

Bas van Velzen (eland@knoware.nl)
Mon, 29 Apr 1996 18:48:32 +0100

>Sulphuric Acid in Peroxide
>
>
> "So maybe a chemist could look into this
>test again and give some extra information if the ammonia will change the
>o"
>
>Surely as we are talking about tiny amounts of sulphuric acid, less than 0.1%,
>in a tiny area for a very short time where the print has already spent a
>relatively long time in a bath of 1 or 2 % HCl before washing, the effect of
>the
>sulphuric acid, if any, in the peroxide is going to be de minimis. The lesson
>here , in modern platinum practice, is never let HCl near your platinum prints.
>
>A story to upset the conservation police. A rather ridiculous set of
>circumstances once led me to pour concentrated sulphuric acid over a platinum
>print. There is a small hole where the acid hit the paper but there was no
>obvious effect on the platinum of the print. I use the print as a warning to
>students to put acids in the right, ie poison, bottles and ensure that they are
>clearly labelled.
>
>Terry King

indeed we are talking about very small amounts of the acid but
sulphuric acid can damage paper especially when left to dry on/in the
paper, I witnessed this in a test where we looked into what would happen
when peroxide without ammonia was used to bleach spots. So be sure to
blotter off the drop and in case of doubt rinse (another drop and blotter
action) with some pure tap water (there are always some calcium and
magnesium salts present in tap water = deacidification). On second reading
this only answers half of my remark: will ammonia hamper the spot test?
because when it is not what is there against adding a drop or two?
It maybe nice to know that transparant paper used to be made by
actually leading a roll of paper through a sulphuric acid bath followed by
an immediate rinse in an alkaline bath and further rinsing. On the other
hand these kind of papers cause a hell of a lot of trouble in archives,
libraries and the like because the dP (degree of polymerisation) of the
cellulose has become so low by this treatment that they become very, very
brittle on ageing.

Bas van Velzen

PS. the name "conservation police" was coined by Judy and is not exactly
what I think my role should be. It was fun while it lasted, at least the
police bit. Maybe "conservation impromptuist" would be better, any
suggestions? :-)

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