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Thanks Gustav and all for these interesting discussions; for the
holothurians from Eparses Islands that I determined recently,  I used water
as it is easy, but you are right it would be better to have a medium which
allows the best conservation for future!
Best
Chantal


2014-07-22 15:37 GMT+02:00 Paulay,Gustav <[log in to unmask]>:

>  Hi All,
>
>
>
> Thanks for all the suggestions.  I have looked a bit further, and although
> I do not fully understand the optics (but will find a microscopist to talk
> to…), the issue seems to be that calcite is birefringent – i.e. has two
> refractive indeces (RIs), at 1.4-1.6 and 1.5-1.9 (depending on light wave
> length), so how bright an ossicle looks depends on how these axes are
> oriented.  The problem is striking when you look at, for example,
> Holothuria with three dimensional buttons, where some buttons happen to lie
> on their “side” while others lie on their “back”.  Some buttons are then
> really well defined and others faint.  It is not apparent (though ossicles
> can look faint depending on their orientation) when viewing ossicles that
> all lie in the same orientation, as their optical axes then form the same
> angle with the viewing axis.
>
>
>
> The problem appears to be worse when IR of the mounting medium is close to
> that calcite, which is the case with basically all the mounting media we
> usually use, as manufacturers strive to have RIs match that of glass
> (1.52).  Refractive indeces of Euparal=1.48, DPX=1.52, Canada Balsam=1.54,
> Permount=1.54 all fall in this range, and although I have not tried them
> all, I suspect all have this problem.  Yves – this issue is clearly visible
> in your slides – e.g. see the fuscogilva type slides:
> http://www.echinodermata.be/index.php?option=com_content&view=article&id=96:holothuria-fuscogilva&catid=25:paris&Itemid=48
>
>
>
> Other issues include the crystallization with age of Permount Dave
> suffered from (which supposedly has been fixed, but I remain vary), and the
> acidic nature of Canada Balsam.  I just checked some slides we made in CB a
> few years back and indeed the ossicles are dissolving.  Immersion oils also
> strive to have RI of glass, plus they do not provide a permanent mount.
>
>
>
> RI of water is 1.33, so ossicles look much better in a simple wet
> preparation than in the permanent mount, a useful trick if you are
> producing photos for a pub.  However in the long run it would be ideal to
> have a mounting media that is archival and has an RI that makes ossicles
> nicely and uniformly visible.  I am not sure if a product like that is
> available.
>
>
>
> Cheers – Gustav
>
>
>
>
>
> *From:* flmnh-aspidolist [mailto:[log in to unmask]] *On
> Behalf Of *Yves Samyn
> *Sent:* Monday, July 21, 2014 2:48 PM
> *To:* [log in to unmask]
> *Subject:* Re: mounting medium
>
>
>
> Hi Gustav
>
>
>
> Euparal does the trick to me.
>
>
>
> In an earlier life I used DPX to save histological preps; perhaps this
> works on ossicle preps as well (
> https://ie.vwr.com/app/catalog/Product?article_number=360292F). Canada
> balsam seems fine too, but gives some decoloration...
>
>
>
> cheers - yves
>
>
> -----Original message-----
> *From:* SCOTT SMILEY <[log in to unmask]>
> *Sent:* Mon 21-07-2014 15:52
> *Subject:* Re: mounting medium
> *To:* [log in to unmask];
>
> Dear Gustav
>
> Cargil (I think it was Cargil) used to make a High Viscosity Oil that was
> fluid enough, when gently heated on a hot plate, to hold the coverslip down
> and did not crystallize. I do not know if it is still available.
>
> Scott
>
>  On 7/21/14, 4:17 AM, Paulay,Gustav wrote:
>
>  Hi All,
>
>
>
> I have been using Euparal for some time now as the mounting medium for
> cuke ossicles.  It does not have the crystallization – age problem of
> Permount.  However it has the wrong refraction index, so that some of the
> ossicles that have their optical axes in the “wrong” direction appear much
> fainter than others in these preps.  In contrast the same ossicles look
> terrific when viewed in just water.  Does anyone know of a better
> alternative – i.e. a permanent mounting medium without these optical issues
> that also does not crystallize?
>
>
>
> Thanks – Gustav
>
>