Re: Gum chemistry is simple and easy and Gloy

I didn't know what David was referring back to, but since it was
about gloy, I decided it must have been Terry, so I looked in the
junk folder and here it was. (My mail program puts anything with an
aol address into the junk automatically.)

Now let me see.... ladders.... bits sticking out....atoms break
off... more pigment makes the gum less soluble.... simple as pie!

Actually, the chains and ladders part is fairly true of PVA, though
it's not true of gum at all. Gum comes in globular structures that
are highly branched within; this dense compact structure is what
makes gum capable of forming concentrated solutions with relatively
low viscosity, the experts in gum arabic tell us.

Atoms break off? The high school chemistry text you're working from
needs updating, Terry, if that's what it says.

I could say more about the rest, but it's too nice a morning to sit
at the computer. I'll just say this is a perfect illustration of
the point I was making: people can make fine gum prints even if they
don't understand anything about the process, or even if what they
think they know about it is wrong, oversimplified, or outdated.

Katharine

On Mar 20, 2006, at 1:46 AM, TERRYAKING@aol.com wrote:

> In a message dated 19/03/2006 20:57:13 GMT Standard Time,
> kthayer@pacifier.com writes:
>
> I do agree with another statement in the above-referenced post, to
> the effect that knowing how the gum process works won't make anyone a
> better gum printer,
>
>
> On the contrary, understanding how things work gives a better
> understanding of how they should be done.
>
> Again, the principle of how gum dichromate works is simple.
>
> Long chain molecules of gums, with bits sticking out of the
> side.like a ladder with a central upright,. are flexible; this
> flexibility makes the substance soluble.
>
> The dichromate molecule is unstable, atoms break off when they are
> exposed to powerful energy such as UV light.. The atoms which break
> off join up the rungs of the ladder of the gum making it
> inflexible. That inflexibility renders the substance insoluble.
>
> The longer the exposure the more insoluble the substance becomes,
> i.e. less contrast. The more pigment that gets in the way of the
> UV light, the less insoluble the substance becomes, i.e. more
> contrast.
>
> See my web site and the introductory chapters of any good high
> school chemistry text book up to .the chapters on the structure of
> molecules and the periodic table.
>
> As to PVA we have made a substitute for Gloy which gives multiple
> exposures with acrylics..Knowing how it works helped us to do so.
>
>
> Terry
>
>
>
>
> Terry King FRPS
>
> RPS Historical Group (Chairman)
>
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> 1. An excellent thing is as rare as it is difficult.(Spinoza)
> 2. A man's reach should be beyond his grasp or what's a heaven for.
> (Browning)
> 3. Frustra fit per plura quod potest fieri per pauciora.(Occam's
> razor or 'Keep it simple!').
> 4. Nullius in Verba (Horace), 'Take no man's word for it' (motto of
> the Royal Society).
> 5. If ignorance is bliss, why are not more people happy ? (anon)
Received on Mon Mar 20 12:44:34 2006