"If you measuring such a small thing on the same kind of spring scale
at the sea level and at 500m above the sea level, the scale will show
you a different result. Simple example:"
Hi Sergey,
I think you want to clarify that. If you try to measure something that
weighs 0.001 grams ( 1 mg ) at sea level vs. 500 meters higher, it will
weigh 251 ng (nanograms) less, but still 1.000 mg = 0.99975 mg. That is
not detectable by any conventional scale and other external factors
like differences in air density, air saturation, convection, not to
mention people walking around nearby, etc. will swamp the difference,
not to mention the porosity of the sample itself which is a problem for
even the regular fare.
But - I think you meant trying to weigh something with the precision of
1 mg for macro sized samples is very difficult. In the case of a ten
gram sample the 251 nanograms becomes 2.5 milligrams of difference, and
you are right!
Kindest wishes
Doug
-----Original Message-----
From: Sergey Vasiliev <vs.petrov...@gmail.com>
To: Michael Blood <mlbl...@cox.net>; Met. Mike Bandli
<fuzzf...@comcast.net>; 'Michael Farmer' <m...@meteoriteguy.com>
Cc: Meteorite List <meteorite-list@meteoritecentral.com>
Sent: Fri, Jul 1, 2011 5:24 pm
Subject: Re: [meteorite-list] Micromounts and weights - Standards Vary
Hi All,
Actually I always thought that trying to measure something like 0.001g
is
very difficult.
If you measuring such a small thing on the same kind of spring scale at
the
sea level and at 500m above the sea level, the scale will show you a
different result.
Simple example:
http://www.edinformatics.com/math_science/mass_weight.htm
Best,
Sergey
-----Original Message-----
From: meteorite-list-boun...@meteoritecentral.com
[mailto:meteorite-list-boun...@meteoritecentral.com]On Behalf Of Michael
Blood
Sent: Friday, July 01, 2011 11:03 PM
To: Met. Mike Bandli; 'Michael Farmer'
Cc: Meteorite List
Subject: Re: [meteorite-list] Micromounts and weights - Standards Vary
Mike,
I checked this out and was confused. The first statement:
" METTLER TOLEDO AT261 0.01mg Counting Scale in HardCase"
Implies accuracy down to a tenth of one mg! That is .0001g
HOWEVER, the first part of the description reads:
Weighing Capacity:205g Repeatability:(0-50g)+/-0.015mg
Linearity:(10g)+/-0.03mg Stabilization:(typical)8-12sec
What the h*** does that mean? It sounds like a maximum
Capacity of 205g, but "repeatability:(0-50g)+/- 0.015" seams
Like it is saying it can be off by 15mg!
THEN: "Linearity:(10)+/- 0.03mg Stabilization..." sounds
Like they are saying it could be off by 30mg.
How do others read this?
Michael
On 6/30/11 5:11 PM, "Met. Mike Bandli" <fuzzf...@comcast.net> wrote:
Yes, and for those serious about weights, I would highly recommend a
refurbished Mettler unit similar to this one:
http://tinyurl.com/3dz8udc
----------------------------------------------
Mike Bandli
Historic Meteorites
www.HistoricMeteorites.com
and join us on Facebook:
www.facebook.com/Meteorites1
IMCA #5765
-----------------------------------------------
-----Original Message-----
From: Michael Farmer [mailto:m...@meteoriteguy.com]
Sent: Thursday, June 30, 2011 4:55 PM
To: Mike Bandli
Cc: Michael Gilmer; Meteorite List
Subject: Re: [meteorite-list] Micromounts and weights - Standards Vary
I use a multi-thousand dollar scale, you are right about the cheap
scales,
have bought several for the field, they are worthless.
Wanna sell the small stuff, make the investment to do it right.
Michael Farmer
Sent from my iPad
On Jun 30, 2011, at 4:52 PM, "Mike Bandli" <fuzzf...@comcast.net>
wrote:
A little perspective on milligrams:
There are a lot of meteorite mg weights out there that not accurate.
We
can
thank these new, cheap Chinese digital scales that promise
accuracies of
+/-
1mg or less, which are a complete joke. I bought one in Tucson to
test it
out against my high-end calibrated machine and it was off by about
10 mg
on
average for pieces 50 to 100 mg and 5 mg on average for pieces 10 to
50
mg.
Anything fewer than 10 mg - forget about it. The calibration weights
it
came
with were even more laughable...
In reality, in order to be able to accurately measure mg, you need a
machine
that has been recently leveled and calibrated in-situ. I have a
recently
leveled/calibrated mechanical scale whose tare changes by the hour
due to
changes in the weather. It even picks up the subtle vibration of the
dishwasher downstairs.
Bottom line - a $100 mg scale isn't going to get you the accuracy
needed
to
accurately measure true mg. Since most people can't afford the
hundreds
to
thousands it costs for an accurate mg scale, I don't expect most mg
weights
advertised to be truly accurate. They're close...
Just my 2 mg worth (+/- 1mg)...
----------------------------------------------
Mike Bandli
Historic Meteorites
www.HistoricMeteorites.com
and join us on Facebook:
www.facebook.com/Meteorites1
IMCA #5765
-----------------------------------------------
-----Original Message-----
From: meteorite-list-boun...@meteoritecentral.com
[mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of
Michael
Gilmer
Sent: Thursday, June 30, 2011 4:17 PM
To: Meteorite List
Subject: [meteorite-list] Micromounts and weights - Standards Vary
Hi Listees and Micronauts,
There has been some discussion recently about people buying
micromounts from a vendor on eBay and not getting the weights they
were promised. I thought I would throw out some thoughts on micros,
since those are my bread and butter.
First, the definition of "micromount" is relative. There is no
set-in-stone size bracket for what defines a micromount. It seems to
me that the general consensus is that micromounts are in the 1g range
for the more common types and sub-gram in weight for the rare types.
Very rare falls or planetaries are commonly sold by the milligram.
Rockhounds tend to equate meteorite micromounts with mineral
thumbnails. But generally speaking, most micromounts on the market
today are in the sub-gram (<1g) range.
Ideally, a micromount should be visually appealing (such a well
polished, thin part slice with good surface area to weight ratio) and
big enough to identify the lithology of the type/fall, while at the
same time being cheap enough to afford on a limited budget.
The more preparation that goes into making a given micromount, the
higher the price, generally speaking. At some point, it's not
financially viable to put a lot of cutting and polishing work into
piece of common find that is only worth a buck or two a gram.
Smaller micros are difficult to work with during preparation, for
obvious reasons, so many of the micromounts seen on the market are
unpolished, rough, or broken.
What motivates a person to collect micromounts varies from person to
person, but the most commonly cited reason for buying micros is to
temporarily fill a void in a type collection. It could be a
petrologic type, a find from a given geographic area, a fall from a
specific date, etc. Often a micromount is a temporary measure until a
nicer specimen can be acquired, or until the needed finances to buy a
larger piece can be saved up. For the very rare types and
planetaries, a micromount might be the best hope for a collector on a
restricted budget.
There are a couple of schools of thought when it comes to dealing and
selling micromounts - some dealers sell specimens by weight (by
milligram, even for specks) or some dealers offer specimens by the
piece (by eye/photo). For the most part, I am of the latter school
that sells micros by the piece. That means I don't weigh each and
every micromount, unless it is a very rare and valuable meteorite
such
as a planetary or historical fall. Each dealer has their own methods
for handling micromounts and we those aren't really relevant to the
discussion at hand.
When weighing micromounts, one must use an accurate scale that is
sensitive to 1 milligram - the good ones are used by diamond and gem
dealers. There are many brands of these scales which range in quality
and accuracy. When dealing with small specks that weigh a milligram
or two, the readings can vary from unit to unit when weighing the
same
specimen. If a buyer pays for and is promised a micro that weighs
100mg, it better weigh 100mg and not 50mg or 80mg. Sometimes a buyer
gets an added bonus because their personal scale is more accurate
than
the seller's scale and a promised 100mg micro might weigh 120mg or
150mg. If the seller is not sticking to a strict pricing scheme ($/g
or $/mg), then ultimately what matters is if the buyer is happy with
their micromount.
From a collector's standpoint, it pays to shop around for
micromounts.
Unless it's a very rare meteorite, it's easy to find several dealers
offering similar-sized specimens for widely-varying prices. One must
also pay close attention to the reputation of the seller and the
provenance of rare specimens. Because micros tend to be small (some
are downright tiny), it would be easy for an unscrupulous seller to
misrepresent specimens as something more valuable than what they
truly
are. Chances are, if you are reading this mailing list, you are one
of those people who can find a reputable source and who does their
homework before sending payments across oceans on fiber-optic cables.
My own personal meteorite collection (the pieces I keep in my cabinet
and are not traded on my website) are mostly micromounts and I keep
the majority of them stored in 1.25" gemjars with paper labels inside
the bottom, under the foam. Some people prefer membrane boxes, small
Riker boxes, or other storage and display methods, but that is the
subject of an entire debate of it's own. The most commonly-seen
container on the micromount market is the gemjar, and thus it is a
general rule of thumb that if a specimen will fit into a gemjar, then
that specimen could/should be called a "micromount".
Best micro-regards,
MikeG
--
-------------------------------------------------------------------------
-
--
-----
Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
Website - http://www.galactic-stone.com
Facebook - http://tinyurl.com/42h79my
News Feed - http://www.galactic-stone.com/rss/126516
Twitter - http://twitter.com/galacticstone
EOM -
http://www.encyclopedia-of-meteorites.com/collection.aspx?id=1564
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