[meteorite-list] Micromounts and weights - Standards Vary

From: Michael Gilmer <*meteoritemike_at_meteoritecentral.com*> Date: Fri, 1 Jul 2011 09:24:29 -0400 Message-ID: <BANLkTinFghNfmvVGRfimWJTXF+rB_azUhA_at_mail.gmail.com> · meteoritemike_at_meteoritecentral.com

-- 
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Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
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On 7/1/11, MexicoDoug <mexicodoug at aim.com> wrote:
> 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
>>
>> --
>>
> -------------------------------------------------------------------------
> ---
>> -----
>> 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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