Re: gloy for tricolor on yupo?

On Mar 30, 2006, at 11:44 PM, Loris Medici wrote:

> mate - since my lightsource is twice as
> strong as hers, it makes sense that my exposure time is close to hers
> even I use a lower dichro concentration).

Okay, it looks like I was reading a categorical statement where you
didn't mean one, so I think we're in agreement here.
>
>
>> "...But I use saturated ammonium dichromate and I live in a very
>>
> humid climate, which together probably account for most of the fact
> that I can print a very sturdy layer in a short time. If I were
> using potassium dichromate, or diluted ammonium dichromate, or if I
> were living in a drier climate, exposure times to make a sturdy layer
> would be longer (and in fact my times are longer during rare dry
> spells here."<
>
> Type of dichromate should be completely out of equation given the
> molecule count per volume of coating solution remains the same.

That's what I thought, until I read this study, which started from
the observation: " It has been established for a long time that
holograms formed from ammonium dichromate as a doping chemical were
of better quality than those obtained with potassium dichromate. So
far, no satisfactory explanation has been given to this experimental
observation. Thus the aim of the work [in part] was to determine...
the specific role played by ammonium cations: why does ADC doped PVA
yield better holograms than KDC doped PVA?" They calculated the
weight of the two dichromates to "obtain the desired chromium
percentage in weight respectively which corresponds to the same
ratio, Cr(VI)/PA unit" for each of the dichromates, and found that
even at the same "molecule count per volume" as you say, the ammonium
dichromate created a more stable image; they concluded that the
"improvement brought by ammonium dichromate with respect to potassium
dichromate involves amide groups as additional chelating sites for
chromium (V) resulting in the increase of the matrix crosslinking."

Bolte etc al "Hologram Formation Reconsidered in Dichromated PVA:
polymer crosslinking around chromium (V)." in Practical Holography:
Materials and Applications, SPIE proceedings 2005.
>
>
>> "Loris, I didn't ask if you thought it should work, I asked if you
>>
> knew anyone who had done it. But I think maybe a couple of things are
> being confused here. As to coating, I can coat yupo with gum easily;
> the issue for me with gum and yupo isn't the adhesion of the coating
> to the yupo but the adhesion of the hardened gum to the yupo, which
> is a completely different issue."<
>
> But what makes you think: the PVA which adheres perfectly to the
> substrate before exposure should (or may) loose that property when
> hardened?

Well, goodness, I don't just "think" that;, I know it from much
experience coating glass and yupo and mylar with nice smooth even
coats of gum that "adhere" to the substrate beautifully but then in
development the hardened gum floats off into the water. This
knowledge that the adherence of the coating and the adherence of the
hardened gum are two different issues is a product of experience, not
just a speculation.
Katharine
Received on Fri Mar 31 09:20:47 2006