[Nhcoll-l] Alcohol concentrations for preserving flowers

[Dirk Neumann]

... it might be worth adding that some denaturants as some ketones are 
also used as component in chromatography and extract pigments quite well 
(not all, put some). Natural colours can be caused by quite different 
effects and sources, e.g., pigments, unsaturated [metal] ions as key 
element in chelating agents, optical refraction on crystals embedded in 
tissues, etc..

Often, the effect of visual colour we see in the specimens we collect is 
caused by electron excitation in biomolecules, which cause changes in 
the bonding or chemistry of respective molecules. Most of our fixatives 
and storage fluids tend to be highly polar, and through polarisation or 
depolarisation of respective biomolecules, colours usually fade - cf. 
colour reaction in many indicators we use.

There are few natural pigments that are stable, but admittedly few. And 
I would always be careful with bright coloured, historic teaching 
specimens prepared around 1900 ... As old bold bright paints, the 
ingredient are rarely healthy (and usually containing heavy metals such 
as cadmium, chrome, lead, etc.)

With best wishes
Dirk


Am 10.05.2021 um 20:10 schrieb John E Simmons:
> Gretchen,
>
> I was hoping that a botanist might respond on the list with a 
> recommendation for you (botany is not my specialty). I can tell you 
> that the original Kew mixture was 53 percent industrial methylated 
> spirits (IMS, which is ethyl alcohol containing 9 percent water and 
> 2–4 percent methanol), 37 percent water, 5 percent formalin (“dilute 
> formaldehyde”), and 5 percent glycerol (Forman and Bridson 1989).
>
> A note in the second edition of /The Herbarium Handbook/ (1992) stated 
> that due to controls on hazardous chemicals, the original formula at 
> Kew had been withdrawn and replaced by a mixture of “70% alcohol 
> (ethanol, or ethanol + trace of methanol), 29% water and 1% glycerol. 
> If using 90% strength Industrial Methylated Spirit (IMS) the mixture 
> is 78% IMS, 21% water and 1% glycerol. With different strengths of IMS 
> the proportions must be adjusted accordingly” (Forman and Bridson 
> 1989, 210).
>
> In the third edition (Bridson and Forman 1998) the Kew mixture recipe 
> was ten parts IMS, one part formalin, one part glycerol, and eight 
> parts water.
>
>
> The Kew mixture was supposed to help preserve the color in plants. If 
> your concern is just to preserve flowers sufficiently for them to be 
> dissected, you might try 70% ETOH, with no other additions. If the 
> specimens are not intended to be saved as museum specimens, you could 
> use denatured 70% ETOH, which is considerably less expensive.
>
>
> Hope this helps.
>
>
> --John
>
>
> John E. Simmons
> Writer and Museum Consultant
> Museologica
> /and/
> Associate Curator of Collections
> Earth and Mineral Science Museum & Art Gallery
> Penn State University
> /and/
> Investigador Asociado, Departamento de Ornitologia
> Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima
>
>
> On Fri, May 7, 2021 at 4:37 PM Gretchen Meier <gameier at d.umn.edu 
> <mailto:gameier at d.umn.edu>> wrote:
>
>     Hi there!
>     Is there a recommended ETOH concentration for preserving flowers
>     for later dissection? In a pinch, I've used cheap vodka (about
>     40%) but I'm not sure I want to bring that into a classroom.  Any
>     suggestions?
>
>     -- 
>     Gretchen Meier (/she/her/hers/)
>     Olga Lakela Herbarium (DUL)
>     University of Minnesota Duluth
>     gameier at d.umn.edu <mailto:gameier at d.umn.edu>
>     218.726.6542
>
>     /Naturum expellas furca, tamen usque recurret - Homer /
>     'you may drive nature out with a pitchfork, but she will come
>     hurrying back'
>
>
>
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-- 


Dirk Neumann

Tel: 089 / 8107-111
Fax: 089 / 8107-300
neumann(a)snsb.de

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81247 München

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---------

Dirk Neumann

Tel: +49-89-8107-111
Fax: +49-89-8107-300
neumann(a)snsb.de

postal address:

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