Re: gum arabic

[Jack Brubaker <jack@jackbrubaker.com>]

Loris, There are three questions here. Does gum when used as a pigment binder have a long and effective history with little or no record of darkening? I think the answer is yes. Is a  thick layer of gum used as a varnish wise? The Williamsburg example says no. Is hardened gum going to darken over time? Beyond the 120 years that it has been know to be used we don't know.

My point was not to assert that hardened gum was not going to discolor. I just feel that the Williamsburg example of gum used as a varnish while interesting it is not proof of anything directly relevant to gum printing. I see your concern for our finite information on hardened gum. It would be nice to have more info on hardened gums durability. My response was to point out my opinion that the example of gum as a pigment binder going back to ancient times is more like our practice of printing than an example of a thick layer of gum used as a varnish. 

Sorry if I was not clear,

Jack

2009/1/31 Loris Medici <mail@loris.medici.name>

But in a gum print the gum and the pigment(s) are inseparable. So, to me
your point (about the color change of the pigments) is irrelevant. Also
the writing doesn't say anything about the failing of the binding. (=
Loosing binding properties, to me.)

What are your arguments giving you such a concrete opinion that hardened
gum won't darken with age? That is the information I specifically need.

BTW, I'm not saying that hardened gum will definitely darken with time.
I'm just concerned about this possibility now, being aware of that
specific account.

Hope I'm making myself clear.

Regards,
Loris.


31 Ocak 2009, Cumartesi, 4:15 am tarihinde, Jack Brubaker yazmış:

> There is no comment here about the original watercolor image having
> changed
> color. It is just the inappropriate use of gum as a varnish that has
> failed.
> There are many examples of gum being used as a binder going back much
> further without failure. Generally the only concern with really old
> watercolor painting is the viability of the pigments used at the time.
> Jack
>
> 2009/1/30 Loris Medici <mail@loris.medici.name>
>
>> Maybe, but they're also talking about darkening (cracking is another
>> issue) and that's my actual concern -> can it happen to hardened gum
>> also?
>>
>> Anyway, we know that gum prints are stable for at least 120 - 130 years
>> (by looking to the condition of actual prints made in the late 19th
>> century), which is fine. But the image on the page is around 2-2.5 times
>> older than the oldest gum dichromate print we can inspect...
>>
>> Regards,
>> Loris.
>>
>>
>> 30 Ocak 2009, Cuma, 10:57 pm tarihinde, Katharine Thayer yazmış:
>> >> Loris wrote:
>> >>
>> >> I'm not that much confident since I had read this:
>> >> http://www.history.org/foundation/journal/Winter01-02/bird.cfm
>> >>
>> >> What do you (all) think?
>> >
>> > Loris, I think it's unfortunate that they used unhardened gum as a
>> > varnish; soluble gum is extremely likely to crack, as it did in that
>> > instance, as well as being totally water soluble.  (In this case the
>> > water solubility was a blessing, because it made it easy to
>> > remove).   This isn't relevant to our use of gum arabic where the gum
>> > that remains in the artwork is not water soluble and doesn't have the
>> > same properties of being susceptible to cracking, so I'd say you
>> > shouldn't let that account shake your confidence in the archivality
>> > of a gum print.
>> > Katharine
>>
>>
>