FW: Re: Sundial finish

[david . pawley]

> Subject: Re: Sundial finish
> 
> 
> I would say just take a walk around ontdoors and look at the shadows cast by 
> all sorts of objects, and on all types of surfaces. This would give good idea 
> of suitable surfaces for sundials.

> David






> 
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> 
>  
> Message Received: Jun 07 2013, 09:19 AM
> > From: "Frank King" 
> > To: "Art Krenzel" 
> > Cc: "sundial@uni-koeln.de" 
> > Subject: Re: Sundial finish 
> > 
> > Dear Art,
> > 
> > You ask a challenging question...
> > 
> > what surface (color, texture, finish,
> > material, etc) is the best choice to
> > show a gnomon shadow?
> > 
> > This is a big subject and to understand it
> > properly you will need to do some serious
> > study! You can make a start by discovering
> > what a Lambertian Surface is. Essentially,
> > it is a surface which reflects equally in
> > all directions. It is absolutely NOT like
> > a mirror.
> > 
> > In general, a Lambertian Surface is better
> > than a non-Lambertian Surface for sundials.
> > I have seen disastrous dials made of polished
> > stainless steel! The user can get blinded by
> > reflection from the sun.
> > 
> > Stainless steel CAN work but it must have
> > a "satin finish".
> > 
> > I would add that light-coloured surfaces,
> > for example limestone, are better than
> > dark surfaces though, paradoxically, slate
> > is quite good.
> > 
> > These surfaces must not be polished of
> > course. Polished marble is almost as
> > bad as polished stainless steel!
> > 
> > The surface should not break up the shadow
> > and possibly the worst receiving surfaces
> > are long grass and round cobbled pavements.
> > 
> > This is enough to start a discussion.
> > 
> > Let's see what others say!
> > 
> > Frank King
> > Cambridge, U.K.
> > 
> > PS
> > 
> > Try reading these references:
> > 
> > http://en.wikipedia.org/wiki/Lambertian_reflectance
> > 
> > http://en.wikipedia.org/wiki/Lambert%27s_cosine_law
> > 
> > http://en.wikipedia.org/wiki/Oren%E2%80%93Nayar_reflectance_model
> > 
> > ---
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> > 
> > ---
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Re: Sundial finish

[Kevin Karney]

Dear Art
"Sundials Australia" by Margaret Folkard & John Ward (available via 
www.sundialsaustralia.com.au) has an interesting chapter on this subject
Best wishes
Kevin Karney

On 6 Jun 2013, at 19:49, Art Krenzel  wrote:

> There have been several discussions on the optimum shape of a gnomon to 
> produce a good shadow however I have not seen any discussion on the optimum 
> surface coating of a sundial yet.
>  
> From the collective experience of this listserve, what surface (color, 
> texture, finish, material, etc) is the best choice to show a gnomon shadow?
> 
> Art Krenzel
> 
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> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial

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Sundial finish

[Art Krenzel]

There have been several discussions on the optimum shape of a gnomon to produce 
a good shadow however I have not seen any discussion on the optimum surface 
coating of a sundial yet.
 
>From the collective experience of this listserve, what surface (color, 
>texture, finish, material, etc) is the best choice to show a gnomon shadow?

Art Krenzel

 












 


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