NavList:

   

Reply

Alex:

I'm not an expert on antique instruments, but I can see some clear
reasons for using ivory.

First of all, the relative cost of the materials isn't a large factor
because such a minuscule amount is used in a sextant.

Think of ivory as a 18th century equivalent of a durable white plastic
from today.  It's tough (used to make billiard balls) but easy to
inscribe with calibration lines (which then can be darkened with paint
or ink).

On the other hand, I believe it is a lot harder to get good dark lines
on silver -- before 20th century baked-on paint techniques, paint or ink
just wouldn't stick as well.

Silver also tarnishes (and polishing silver can wear it down as well as
destroy any paint or ink which would wreck the calibration marks).
Ivory, on the other hand, requires much less care.

It's not just sextants, there are a heck of a lot of other instruments
from the period that also use ivory.

Lu Abel

alex wrote:
>
> Why the scales of octants and some sextants
> were made of ivory?
> Does ivory have some favorable heat expansion properties?
> Or any other good physical properties?
> Or what? If I understand correctly that "ivory" is the substance
> made of an elefant's tusk,
> it seems to be that even in 1820-s ivory was not cheaper
> than silver. I could not figure the price, but only found
> that 3,000 cwt (=hindredweight=100 pounds) of ivory
> was sold in 1827 in London.
> I'd guess that silver was cheaper.
>
> On the other hands ivory was used on cheap octants
> and silver (or gold or platina) on expensive sextants.
>
> (Nowadays it is reversed, of course: cheap American
> ebony-ivory-brass octants
> are sold on e-bay for higher price than fancy British sextants:-)
>
> Alex.
>
>
> >
>

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply