Paul Gerhold on thu 26 jun 08
Dear Tim,
When spheres of equal diameter are packed the percentage of void volume is
the same no matter what the diameter of the individual spheres. Therefore if
the clay particles are all of the same density and diameter the density of
the packed spheres will be the same. It makes no difference to the final
density whether the spheres are one micron or fifty microns in diameter. The
density of the fired clay is dependant on the densities of the individual particles
and on the variations in particle diameter. This partly explains why it is
advantageous to mix particle sizes when designing clays for dry and fired
strength.
Paul
**************Gas prices getting you down? Search AOL Autos for
fuel-efficient used cars. (http://autos.aol.com/used?ncid=aolaut00050000000007)
Lee Love on thu 26 jun 08
On Thu, Jun 26, 2008 at 7:56 AM, Paul Gerhold wrote:
> and on the variations in particle diameter. This partly explains why it is
> advantageous to mix particle sizes when designing clays for dry and fired
> strength.
This is the single most important advantage "natural", unrefined clays
have clays mixed from refined, uniformed materials, in strength.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"We are such stuff as dreams are made on, and our little life is
rounded with a sleep." --PROSPERO Tempest Shakespeare
Tim See on thu 26 jun 08
Thanks Paul for adding. That's a great tidbit of info,
hard to get my head around but math wise makes sense
so I'll take your word for it. So a variety of sizes
make a denser clay. Say two clay bodies are made, one
with larger particles the other with smaller.(all
particles in each clay are equal) Would the surface
contact between the particles increases as the
particle size decreases? And would the added surface
contact increase dry strength? And isn't contact the
component that determines strength? The ball example
was just that. Unfortunately it was wrong in terms of
density and void volume of round particles. But when
applied to clay particles that are flat
hexagonal(right?) would it then be true that the
smaller particles would be more dense or does it fall
under the sphere rule? Thank you again for correcting
me. I hope you have some insight on the new questions.
TiM SEE
Syracuse, NY
http://www.youtube.com/profile_videos?user=timseepots
http://www.etsy.com/shop.php?user_id=5467443
Ivor and Olive Lewis on fri 27 jun 08
Dear Paul Gerhold,
Perhaps it is unwise to extrapolate arguments about the packing of
uniform spheres in space to considerations about the best sampling of
mineral fragments to make a durable clay.
It is difficult to criticise your example of the packing of spheres
and the independence of the final result
Except to point out that Spheres can be packed in several lattice
patterns and the relationship between the volume of occupied space to
unoccupied space differs according to the nature of the packing. Which
leads to differences in density (Ex Carbon. Diamond 3.5, cubic,
Graphite 2.1 hexagonal). Then there are radial relationships between
the size of uniform spheres and the next smallest that will fit into
the space between the larger spheres, which is associated with the
coordination number.
Without photographs of samples made with modern scanning electron
microscopes we know almost nothing about the spatial geometry of clay
bodies, be they plastic, green ware, bisque, or mature ceramic.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Vince Pitelka on fri 27 jun 08
Ivor Lewis wrote:
"Perhaps it is unwise to extrapolate arguments about the packing of uniform
spheres in space to considerations about the best sampling of mineral
fragments to make a durable clay. It is difficult to criticise your example
of the packing of spheres and the independence of the final result. Except
to point out that Spheres can be packed in several lattice patterns and the
relationship between the volume of occupied space to unoccupied space
differs according to the nature of the packing."
Ivor -
Technically you are certainly correct about the particle shapes, but the
"spheres" analogy is a good one when discussing the effect of particle size
on plasticity and working structure in claybodies. Certainly the particles
are not really spheres. I am travelling, and thus have not followed this
thread, so forgive me if the following is something that was already
discussed. I expect it was, given the subject line "Density of packed
spheres." The common version is the "Room full of basketballs," which is
full of basketballs but can still accept thousands of golf balls. Then it
could be said to be full, except that it could accept tens of thousands of
marbles and then hundreds of thousands of B-Bs and then millions of grains
of sand. The whole idea has to do with the elimination of unnecessary
voids, which reduces drying and firing shrinkage, and the increase in the
number of contact points between particles, which increases the friction we
rely upon for working structure and also increases dry and bisque strength.
The clay particle has an affinity for water and that encourages lubrication
and slipping that translate to plasticity, but without contact points we'd
have no working structure. A broad distribution of particle sizes (as in
the spheres analogy, but with the variable shapes we would expect in ceramic
materials), is one of the most important considerations in designing the
best claybodies.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Ivor and Olive Lewis on sat 28 jun 08
Dear Vince Pitelka,
Good to hear from you again. Hope you are enjoying your travels.
<< A broad distribution of particle sizes (as in the spheres analogy,
but with the variable shapes we would expect in ceramic materials), is
one of the most important considerations in designing the best
claybodies. >>
....I am in complete agreement . But what is it that cements all
those billions of particles into a solid immobile mass when clay
reaches the "Green" state ???. Once things start heating up then the
best description I know of is that given by Kingery, Bowen and Uhlmann
in their chapter on Grain Growth, Sintering and Vitrification.
Even with a room full of basket balls and filling voids down to the
infinitesimal, the initial packing pattern determines the final
apparent density and shrinkage. Simple cubic packing of uniform
spheres will always give a lower density and greater shrinkage than
the other forms of cubic packing. Working out the optimal size of the
next smallest and subsequent diminution of the object is a task for
the Mathematician.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
steve graber on sat 28 jun 08
ok, i missed this thread till now but want to insert a related question?=0A=
i assume what i missed was using mulitpul sizes of grog to enable the grog =
to fit in each other's shadows or pockets.=A0 that makes sense to me.=0Awha=
t i'd like to know is:=0Awhy is grog generally sand or ground bisque?=A0 =
=0Afor a cone 10 fire, the sand will melt, and the ground bisque-grog will =
continue to shrink at cone 10?=0Ai would think a really strong claybody wou=
ld be finely ground cone10 clay for a grog in with the clay?=A0 =0Ajust cur=
ious.=A0 it's not like i make my own or anything...=A0 =0Asee ya=0A=A0Steve=
Graber, Graber's Pottery, Inc=0AClaremont, California USA=0AThe Steve Tool=
- for awesum texture on pots! =0Awww.graberspottery.com steve@graberspotte=
ry.com=0A=0A=0A=0A----- Original Message ----=0AFrom: Tim See AHOO.COM>=0ATo: CLAYART@LSV.CERAMICS.ORG=0ASent: Thursday, June 26, 2008 5:=
10:14 PM=0ASubject: Re: Developing clay bodies-density of packed spheres=0A=
=0AThanks Paul for adding. That's a great tidbit of info,=0Ahard to get my =
head around but math wise makes sense=0Aso I'll take your word for it. So a=
variety of sizes=0Amake a denser clay. Say two clay bodies are made, one=
=0Awith larger particles the other with smaller.(all=0Aparticles in each cl=
ay are equal)=A0 Would the surface=0Acontact between the particles increase=
s as the=0Aparticle size decreases? And would the added surface=0Acontact i=
ncrease dry strength? And isn't contact the=0Acomponent that determines str=
ength? The ball example=0Awas just that. Unfortunately it was wrong in term=
s of=0Adensity and void volume of round particles. But when=0Aapplied to cl=
ay particles that are flat=0Ahexagonal(right?) would it then be true that t=
he=0Asmaller particles would be more dense or does it fall=0Aunder the sphe=
re rule? Thank you again for correcting=0Ame. I hope you have some insight =
on the new questions.=0A=0ATiM SEE=0A=0ASyracuse, NY=0A=0Ahttp://www.youtub=
e.com/profile_videos?user=3Dtimseepots=0Ahttp://www.etsy.com/shop.php?user_=
id=3D5467443=0A=0A=0A=0A
Ivor and Olive Lewis on sun 29 jun 08
Dear Steve Graber,
Perhaps choosing between using Silica sand, Grog and/or Pitchers
(either Bisque or Vitrified) depends on the results you are trying to
achieve.
Taking Pure silica sand to cone 10 may significantly increase the
vitreous nature of the final ceramic and may assist in enhancing
translucency. Adding bisque grog may sequester excess water from a
rather wet plastic clay and make it workable but this would reduce
plastic strength leading to thicker heavier pots. These fillers add
nothing to the strength of plastic clay.
Using vitrified and glazed grog is a way of reducing overheads and is
common in many industrial systems. In glass works, scrap and wasters
are converted into cullet that is added because of its fluxing
qualities.
Bear in mind that none of these additives shrink as they dry from
plastic to their dry green state. This may lead to fissuring.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
steve graber on sun 29 jun 08
Ivor - very interesting - i can see how silica would add to the virtified n=
ature, melting and sealing the *inside* more.=A0 and of course the use of f=
ully vitrified grog to help reduce shrinkage.=A0 ~ yet allow the rest of th=
e pot to crack here & there by reducing shrink in-between the grog.=A0 =0At=
his sets up a nice test i'm not quite able to run just yet.=A0 i've been us=
ing saw dust in clay to get very lightweight pieces.=A0 and i see they dry =
very slowly compared to regular clay.=A0 it seems the saw dust inside acts =
like it's own sponge and the water doesn't pull out from the saw dust as it=
does from the regular clay.=A0 very different capilary action at the water=
molecule level i bet.=A0 plus i see lower shrink although that's only anec=
dotal.=A0 i really should make some shrink rulers to measure this.=A0 just =
like i should actually measure what i'm doing but i don't bother with that =
yet...=A0 =0Ai have a rock tumbler and like many others lots of scrap cone =
10=A0pots.=A0 many with no glaze.=A0 to smash up a few and make my own cone=
10 grog to go with saw dust would be=A0an interesting experiement.=A0 =0Ai=
'm using 50-50 saw dust and=A0clay.=A0=A0i use the stuff coming off the san=
der into a vacuum system.=A0 my friend the carpenter calls this "milk dust"=
because it sloshes around in his bucket like milk.=A0 i find the clay thro=
ws pretty well yet feels almost like i'm "throwing air" in my hands.=A0 sin=
ce i'm basically cheap i like how i can double my clay=A0scrap by running i=
t thru the pug mill with this=A0saw dust.=A0 perhaps i can also extend my s=
crap=A0and save a scrap yard by adding my trash pots into this mix as well.=
..=A0=A0'in th ebegining" i used pet bedding material and got hard to throw=
clay but VERY awesome organic looking pieces!=A0 great for raku or orcid p=
lanters!=A0 (they leaked).=A0 =0Ai have made mugs and bowls for myself and =
the finished glazed pieces look very normal, although much lighter.=A0 plus=
the wife wants a bunch of brick tiles so i might make use of all this to c=
omplete a walkway soon...=0Asee ya=0A=A0Steve Graber, Graber's Pottery, Inc=
=0AClaremont, California USA=0AThe Steve Tool - for awesum texture on pots!=
=0Awww.graberspottery.com steve@graberspottery.com=0A=0A=0A=0A----- Origin=
al Message ----=0AFrom: Ivor and Olive Lewis =0ATo: =
CLAYART@LSV.CERAMICS.ORG=0ASent: Saturday, June 28, 2008 11:33:55 PM=0ASubj=
ect: Re: Developing clay bodies-density of packed spheres=0A=0ADear Steve G=
raber,=0A=0APerhaps choosing between using Silica sand, Grog and/or Pitcher=
s=0A(either Bisque or Vitrified) depends on the results you are trying to=
=0Aachieve.=0ATaking Pure silica sand to cone 10 may significantly increase=
the=0Avitreous nature of the final ceramic and may assist in enhancing=0At=
ranslucency. Adding bisque grog may sequester excess water from a=0Arather =
wet plastic clay and make it workable but this would reduce=0Aplastic stren=
gth leading to thicker heavier pots. These fillers add=0Anothing to the str=
ength of plastic clay.=0AUsing vitrified and glazed grog is a way of reduci=
ng overheads and is=0Acommon in many industrial systems. In glass works, sc=
rap and wasters=0Aare converted into cullet that is added because of its fl=
uxing=0Aqualities.=0ABear in mind that none of these additives shrink as th=
ey dry from=0Aplastic to their dry green state. This may lead to fissuring.=
=0A=0ABest regards,=0AIvor Lewis.=0ARedhill,=0ASouth=A0 Australia.=0A=0A=0A=
=0A
Kim Hohlmayer on mon 30 jun 08
Dear Ivor,
Does greater density imply greater mass? If this is so, could we compare body densities by comparing the weight of samples with the same three dimensional measurements? Or would the variety of materials used in different bodies negate this method? Would this at least work in bodies of the same composition where the only differences were material particle sizes? Or am I so lost that I am not even close to making sense? Thanks for tolerating my ignorance and helping to enlighten me. --Kim H.
--- On Fri, 6/27/08, Ivor and Olive Lewis wrote:
> From: Ivor and Olive Lewis
> Subject: Developing clay bodies-density of packed spheres
> To: CLAYART@LSV.CERAMICS.ORG
> Date: Friday, June 27, 2008, 3:18 AM
> Dear Paul Gerhold,
> Perhaps it is unwise to extrapolate arguments about the
> packing of
> uniform spheres in space to considerations about the best
> sampling of
> mineral fragments to make a durable clay.
> It is difficult to criticise your example of the packing of
> spheres
> and the independence of the final result
> Except to point out that Spheres can be packed in several
> lattice
> patterns and the relationship between the volume of
> occupied space to
> unoccupied space differs according to the nature of the
> packing. Which
> leads to differences in density (Ex Carbon. Diamond 3.5,
> cubic,
> Graphite 2.1 hexagonal). Then there are radial
> relationships between
> the size of uniform spheres and the next smallest that will
> fit into
> the space between the larger spheres, which is associated
> with the
> coordination number.
> Without photographs of samples made with modern scanning
> electron
> microscopes we know almost nothing about the spatial
> geometry of clay
> bodies, be they plastic, green ware, bisque, or mature
> ceramic.
>
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.
Ivor and Olive Lewis on mon 30 jun 08
Dear Steve Graber ,
I think you are on the right track, as is often said,. "Test,Test and
test again".
The rotational speed of a Rock Tumbler is designed to mix, grind,
abrade and polish but not to chip, fracture and crush. I had my local
Black Smith make up a "Dolly Pot" with a half inch flat steel base and
a one foot length of 4 inch dia by 1/4 wall steel pipe. With q six
foot flat headed crow bar weighing 20 pounds I can crush a pound
sample down to minus 200 mesh and get some good exercise at the same
time.
Steve Harrison, who sometimes makes a contribution to Clayart,
published an excellent set of plans for a Potter's Ball Mill and a
full set of instructions explaining the theory behind the process
under the heading of "Thoroughly Modern Milling". Excellent value for
you dollars.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on tue 1 jul 08
<><>Dear Ivor,
Does greater density imply greater mass? If this is so, could we
compare body densities by comparing the weight of samples with the
same three dimensional measurements? Or would the variety of materials
used in different bodies negate this method? Would this at least work
in bodies of the same composition where the only differences were
material particle sizes? Or am I so lost that I am not even close to
making sense? Thanks for tolerating my ignorance and helping to
enlighten me. --Kim H.<><>
Dear Kim Hohlmayer .
Bulk Density is usually given as Mass per Unit Volume eg grams per
cubic centimetre. The shape of the volume is of no consequence. So if
volume is kept at the same measure when comparing differing materials
there is a greater mass when the density is high .
Things change when material is converted from a solid into a
fragmented state because of gaps between particles. This gives an
apparent density which will be lower than the true density of a solid
example.
Apparent densities will vary when samples are prepared with differing
proportions of a variety of minerals that have differing bulk
densities and different shapes and sizes .
Mixtures like clay bodies and glazes have apparent densities because
of the gaps between the bits. The value will change if air is replaced
by water.
Boiling tests that have been discussed are about finding out the
volume of the spaces between the fragments. The difference in mass
between a water saturated sample and its dry mass measures the volume
of the pores, assuming one gram of water has a volume of one
millilitre. Above a certain value it is assumed the pot will leak.
Below that value seeping should not be a problem. Bulk density is not
an issue.
Hope that answers your concerns.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Des & Jan Howard on tue 1 jul 08
Ivor
We changed the rotational speed of our 1/2 gal 'rock tumbler' so that it
does 'chip, fracture and crush' very nicely thank you.
Des
Ivor and Olive Lewis wrote:
> The rotational speed of a Rock Tumbler is designed to mix, grind,
> abrade and polish but not to chip, fracture and crush. I had my local
> Black Smith make up a "Dolly Pot" with a half inch flat steel base and
> a one foot length of 4 inch dia by 1/4 wall steel pipe. With q six
> foot flat headed crow bar weighing 20 pounds I can crush a pound
> sample down to minus 200 mesh and get some good exercise at the same
> time.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
| |
|
