[meteorite-list] Micromounts and weights - Standards Vary

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Fri, 01 Jul 2011 00:49:09 -0400
Message-ID: <8CE05C154DCBC73-1180-4A0CD_at_webmail-m078.sysops.aol.com>

I have a cheap Chinese scale for which I paid under $20. I never
thought to question its accuracy since I've never been in a position
where 5mg either way made a difference.

But, let me propose a solution for the occasional user who doesn't have
hundreds of dollars burning a hole in their pocket for something they
may not use as frequently as some of the dealers (who may need a
calibrated scale for trade) and isn't keen on loading up on gadgets for
their Swiss beauty. And who is up for some muted MacGyverish fun.

I just cut 23.5 cm X 30 cm of aluminum foil. Mine was from Walmart,
likely the lightest normal weight standard. It weighs 3.1 grams. That
3100 milligrams. It works out to 4.4 mg per square cm. So you can make
your own set of standards that will be plenty accurate for these
purposes. Calculate the areas of your standard set and consider it a
primary standard (do use a decent scale if your repeat what I did for a
sheet of your own aluminum foil. But don't get too worried: if mine
were 3.0 grams instead of 3.1 grams it would still be 4.3mg/cm2.

Now the fun part which you've figured out by now. Use that cheap scale
and put approximately what the scale says the specimen weighs in
standards on the scale. I.e., if you have a supposed 12 mg specimen,
just put 12/4.4= 2.73 square cm, so put whatever you have that's close
to 3 cm2 or just use a razor to trace around your scale cube bottom if
you are in a hurry to make 1 cm2 cutouts. If you put exactly 3 cm2 in
this example on the scale and it says 15 mg, you know your scale is 2
mg too high so just subtract 2mg to normalized the weight to your
standard. Don't worry about the decimals - there rounding anyway and a
ten-thousandth of a gram is a useless measure to you, anyway. As a
matter of fact a mg or two, or even more depending, is iffy depending
on the temperature, humidity etc etc. etc.

Lots of splainin' above but it is really a cinch. A whole lot easier
for me than dealing with a sensitive analytical balance under most
circumstances. Analytical balances are cool but they have to be treated
with incredible respect to be kept in calibration. The element on the
cheapo scales responds to weights in that range so if you do something
like this you will do just as well for the vast majority of purposes
and you can go to WalMart and buy your custom standards for a buck or
so, if you can't raid the pantry for them. Have fun using the heavier
oven gauge foil if you are in a higher weight range - like 50-100 mg.

The only drawback is humidity on the foil so keep it dry! Don't forget,
a specimen in the 10 mg range can easily pick up 20% extra weight in
water, etc. So if you are worried about that accuracy, you ought to be
sticking your specimens in the oven and weighing them hot. Any
analytical chemists here will remember the gravimetric determination of
nickel - same idea.

Good luck

Doug out


-----Original Message-----
From: Mike Bandli <fuzzfoot at comcast.net>
To: 'Michael Farmer' <mike at meteoriteguy.com>
Cc: 'Meteorite List' <meteorite-list at meteoritecentral.com>
Sent: Thu, Jun 30, 2011 8:11 pm
Subject: Re: [meteorite-list] Micromounts and weights - Standards Vary


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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Received on Fri 01 Jul 2011 12:49:09 AM PDT