[meteorite-list] Micromounts and weights - Standards Vary

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Fri, 01 Jul 2011 18:43:03 -0400
Message-ID: <8CE065759D03768-1B2C-4D500_at_webmail-m008.sysops.aol.com>

"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.petrovich at gmail.com>
To: Michael Blood <mlblood at cox.net>; Met. Mike Bandli
<fuzzfoot at comcast.net>; 'Michael Farmer' <mike at meteoriteguy.com>
Cc: Meteorite List <meteorite-list at 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-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at 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" <fuzzfoot at 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:mike at 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" <fuzzfoot at 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-bounces at meteoritecentral.com
>> [mailto:meteorite-list-bounces at 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
>>
>> --
>>
>
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--
>> -----
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>>
> 
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Received on Fri 01 Jul 2011 06:43:03 PM PDT