New Mineral Named After GIA’s John Koivula
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PostPosted: Fri Apr 10, 2009 2:02 pm 
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Bureaus of Weights and Measures, are usually state agencies though there is some certificate, that some balances come with, that seems to mollify them.

I read that at Tucson a few years ago the weights and measures police came in and made people remove any scale that did not have this certificate (which is a big expense for the manufacturer to obtain sort of like UL approval)

Most states will send someone in with a set of calibration weights, and check out your scale and put a sticker on it. The same folks that are supposed to be making sure we get a gallon of gas when we pay for a gallon of gas.
But if they do come you might want to look at and record the class of weights they are using. Mike made reference above to class two and class four weights. They may have a user set that they have had accurately calibrated but it may be to a looser tolerance than a weight YOU might buy if you are not buying a whole expensive set. Or if you happen to be me and have snagged all the good cal weights that have appeared on LabX for the last ten years. There are not too many being put up lately.

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Of course if you are only using your scale for determinations of SG,etc it doesn't matter....BUT it is certainly a benefit to know that your scale is 100% accurate.
I would consider an accurate scale to be so totally fundamental to any activity in jewelry or gemology that I would never settle for anything less than the best i could get my hands on.

I could see where one might need to get a legal for trade scale and an analytical to really use. I have a scale that proudly says its legal for trade. It reads 0-4000 grams in one gram steps.


Last edited by G4Lab on Fri Apr 10, 2009 2:12 pm, edited 1 time in total.

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PostPosted: Fri Apr 10, 2009 2:07 pm 
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A scale that can be regulated by the owner (in California) will NOT qualify for "legal for trade" certification.


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PostPosted: Fri Apr 10, 2009 2:29 pm 
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The plot sickens.

I have found a relatively inexpensive portable "legal for trade" scale that's rated for carat, gram, ounce and grain modes. It's the Presidium PCS-50 LFT and is rated NTEP Class II by the National Conference on Weight and Measures (USA).

Here's the dilemma: it's available from a Florida supplier for $225. Meanwhile Otto Frei sells it for $269 but says theirs is specially certified legal for trade in the state of California, which is where I do business.

Question: I've done business with Frei for years and know them to be trustworthy. But does the manufacturer's legal for trade certification make state certification unnecessary? And if not, what's the legal situation if a CA-certified scale is taken to another state like AZ (Tucson) for trade purposes?

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PostPosted: Fri Apr 10, 2009 2:47 pm 
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One must get their scale inspected in person by a rep from the Bureau of Weights and Measures. If it checks out, you will get a sticker that they will directly affix to your scale.
If it does not comply, you can get it regulated by the manufacturer and then apply again for a follow-up appointment.
I believe that if you have a scale that is certified (with B of W&M sticker)as legal for trade in California it would be accepted anywhere.


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PostPosted: Fri Apr 10, 2009 4:14 pm 
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How much does the state sticker and visit cost??

Do they put seals over the screws that open the case?


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 Post subject: Buying a balance
PostPosted: Fri Apr 10, 2009 11:46 pm 
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Hi all,

Just a few comments on the responses to my post. First, thanks for the warm welcome.

I would caution against buying more accuracy than you need. As a rule, more accurate balances cost more, take longer to use, and are larger and more delicate. I had access to reasonably priced, used analytical balances in good condition. But I did not need 0.0001 g accuracy and wanted a balance that was more compact, more robust, and quicker to use. Many, maybe most, analytical lab balances do not have “weigh below” capability, and if they do, a much larger platform is needed than for small, 0.001 g gem balances.

Don’t even consider a micro or ultramicro balance (these have an accuracy of 0.001 mg or better). They are quite delicate, require good environmental conditions (thermal, vibration, humidity, etc.), and are time consuming to use. I had a Mettler UM series balance in my lab, and it was a great balance, but we used it only for weighing 1 mg or less. Routine maintenance cost $200 per year (one visit). The one time it needed a serious repair, the cost was more than $1000.

In research labs, balances are classified loosely as “gross” or “open” or “top loader” if they are 200 - 1000 g maximum capacity with 0.01 g accuracy, “analytical” for 100 – 300 g maximum with 0.0001 g accuracy, “semimicro” for 100 – 200 g maximum with 0.00001 g accuracy, and “micro” or “ultramicro” for 1 - 10 g maximum with 0.000001 g accuracy or better. Balances weighing more than 1 kg are referred to as “platform scales” or just “big scales”.

Be cautious about buying used analytical balances. Older ones, even some with digital readouts, do not use load-cell technology, but rely on mechanically manipulated internal weight sets. These do not ship well, to say the least. In fact, most analytical balances were originally shipped with a variety of custom internal shims and braces, usually made of plastic, which had to be removed by the first purchasers. The pieces of plastic were generally thrown in the trash. Shipping the balance without these shims is an invitation to damage. Still today, shims or locking levers (much better than shims; they never get lost) are used for shipping many balances. My recently bought Ohaus has a locking lever for shipping. Never transport or ship a balance to new premises without proper shims or engaging the locking lever(s).

Ohaus is now owned by Mettler (actually the company is Mettler-Toledo). Most, maybe all, of their balances are made in a factory in China that is managed by Mettler.

I can’t emphasize enough the requirement to have at least one (better two or three) highly accurate weights (class 4 or better) to check your balance, and do not rely solely on the calibration weight that may have been supplied with the balance. The weights should be in the same ballpark as the gems you will be weighing, and don’t forget to use them periodically. Such weights are much more portable than any balance. If you are visiting a dealer or show and buying a valuable gem or a gem that looks too small for the advertised weight, whip out your accurate weight (with plastic tweezers, of course) and check the dealer’s scale on the spot. If you haul your own balance to a show, you’ll should take the accurate weight(s) with you anyway to check it after transport.

Calibration weights of all classes can be sold with or without certificates of traceability. Expect to pay a lot more if you want certificates. I’ve never bothered with certificates and have always bought my weights from reputable dealers. However, in some circumstances, legal issues may make certificates desirable or mandatory. Weights used in a compounding pharmacy or weights used to certify balances are good examples.

The issue of weighing for trade is tricky, but from a legal, not technical, standpoint. You have to consider the rules in the jurisdiction in which you will be selling. In California, the counties enforce the rules. Our county has not been particular about whether a balance was certified for trade by the manufacturer or outside agency. For a fee, they test a balance and either certify it or not. In the university lab where my wife used to work, the chief technician had all their balances certified by the county every year (the lab wasn’t selling anything; I think it was a comfort factor for him). The county did it, including the cheapest Acculab top-loader and the ancient platform scale. Rules in other jurisdictions undoubtedly vary, and one jurisdiction may not accept the certification of another, especially between states. I have no idea what the requirements might be for interstate trade or for different gem organizations.

Mike


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PostPosted: Sat Apr 11, 2009 2:50 am 
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I would respectfully disagree with you about buying more accuracy than you need. In particular if you are doing Specific Gravity or Density measurements you are getting your final answer from the ratio of two measurements.

Dr. Hanneman pointed out about twenny years ago that as the size of the stone goes down the error band gets much broader for a balance with a particular sensitivity. Perhaps he would care to post that picture from his book "Guide to the Perplexed and to Affordable Gemology"

Mineralab has summarized this information in conjunction their specific gravity kits here.

My opinion is that for digital gadgets generally you want an order of magnitude more accuracy than you need so that you can trust the digit that is at the level you need. Interestingly the Acculab scales sold by Mineralab are similar to the ones I recently worked on and in fact when I called their service dept. I was surprised to be patched through to Sartorius service who now owns Acculab. They are also made in the far east. They offered to trade in ours for the ones Mineralab has for $165.

One should also be careful in being too prejudiced about this or that measurement principle. The important thing is how much care did they use in implementing it. My observation has been that if you buy Mettler or Sartorius units AND make sure the seller locks them for shipping you will get a good balance most times. That said I do have a predecessor of your UM sitting on the shelf. It is a combo of mechanical and electronic (rather than the old optical scale) but it had taut band suspensions and I think they were gone before it ever got to the fairly reliable surplus dealer I bought it from. At worst I will pull all the class S weights out of it and pitch it. I am going to challenge a clockmaker I know to replace the taught bands and see if it will calibrate. The load cell method is a good method but not the only method. I have a balance made by Denver Inst. (now also owned by Sartorius) that uses electromagnetic current to return the platform to original position when loaded. It proves quite accurate.

I would also like to propose something different from taking your good weights with you when you go out into the field. Mine aren't ever going to leave my bunker. But if you have a balance you have just checked or can go back to your lab where they have the UM series you could calibrate a series of cheap weights and use those as field weights. That way if they develop legs and walk or some goofball mishandles them you wont be out what you spent on the good weights. Cheap weights are almost free these days.

I always urge people who ask me to buy Mettler or Sartorius or a few other brands that are made in the US or Japan (Denver, and, Fisher[made by Denver]) As with microscopes the chinese are undoubtedly going to be a force to be reckoned with but at this moment I don't know if they are ready for primetime. The three Acculabs I had apart were as identical as peas in a pod. they were nicely made with an aluminum cantilever and solid state strain gauges for measuring. But there was no adjustment. You put it in calibrate mode and set a 100 gram weight on it and that is it.

By comparison my Denver can be put into calibration mode and it will sense the weight of the cal weight and set itself to that weight. And there are actually some circuit adjustment trimmers on the circuit board. Denver emailed me a pdf of the service manual. By contrast Acculab has no service manual for the units we have.

I would also like to step back up onto my soapbox and say a word for old mechanical balances. These can usually be obtained for free or if bought they never are more than $50. The typical single pan analytical balance will weigh 50 grams or 160 grams or 200 grams depending on model.
They have an optical scale that reads one miligram per division. And most of them can divide that milligram into 100 parts with a micrometeter optical arrangement. These usually are stuffed with Class S weights or at least S-1 and though they can require a little mechanicking to set up , zero and calibrate , once you do that work they are accurate and pretty rugged and trustworthy. I have three of them around here and I can't bring myself to get rid of them

If you read the NIST documents on scales which include prescription balances and jewelers scales (on the same chart with railroad car weighers , livestock scales and vehicle scales) you see that they look at the weight range from zero to full scale and also how many increments they divide that range into. This is one area where I have a problem with cheapo scales.

If you go to buy a voltmeter for electronic service the entry level for ME anyway is a digital readout of 20,000 counts or 40,000 counts also known as 4 and a half digits. When you start wanting to go higher than that say one count in a million (to read one microvolt in a one volt range.) then they start getting very expensive. I don't believe the balance guys know anything the test meter guys DON'T know about digital measurements.

If you buy quality you rarely have reason to regret it. I agree with you 1000% about obtaining and regularly using accurate calibration check weights. I would never take those out of my house for any reason. Too expensive to replace.


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PostPosted: Sun Apr 12, 2009 4:36 pm 
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I agree that if you want to do specific gravity determinations on small stones using water immersion, better than 0.001 g accuracy will be needed. But, I still hold with the advice to not buy more accuracy than you need. If you need 0.0001 g accuracy (“analytical balance”), then that is what you go for. But in this case, buying a semimicro or micro balance would generally not be desirable because of weight, delicacy, expense, etc.

There are some interesting and useful aspects to errors in SG determination, including the advantages using of liquids other than water. A number of papers on the topic have appeared in the archaeological literature. Maybe someone could summarize it for us or at least point me to an existing summary.

I move my class 2 weights (2 of them) around, but they are protected in their little baggies which, in turn, are in are rigid plastic containers, and I am the only one who touches them. I certainly feel I can move weights around with less potential for damage than a balance. The pair of weight cost $50, which is a lot less than my $250 carat balance. But after reading G4Lab’s post, I’m feeling a little paranoid, so I think I’ll buy a 500 mg class 2 weight ($20) for travel and leave the others at home.

It’s interesting that weight (mass, actually) is the only basic unit for which the ultimate standard is an artifact (a chunk of metal in France). All other units (time, length, etc.) are based on natural properties.

I remember the old taut wire balances (also called torsion balances). My father was a pharmacist, and they were popular in pharmacies until electronic balances took over in the 1980’s. They were never popular in the pre-electronic research labs I inhabited. Triple beams were used for 0.01 g accuracy, and enclosed double or single pan fulcrum balances were used for better accuracy. The fulcrums and the pivot bases of some were made of a mineral, but I’m not sure which one. The ones I saw were colorless and translucent. Does anyone know which mineral it was?

Mike


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PostPosted: Sun Apr 12, 2009 9:32 pm 
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Aaahhh another old geezer :lol: :lol: :lol:

The fulcra and planes were made of either 1)tool steel 2) Agate or 3) synthetic sapphire.

I have a tool steel knife edge Henry Troemner Prescription Balance that I refinished in about 1970.

I had a taut band suspended similar balance which I sold at a camera show about 15 years ago It was quite accurate to about 10mg or so depending on the load.

There is literature even gemological discussing using liquids heavier than water for density measurements. Mercury has been used. And Methylene Iodide as well. I have never tried any of these methods.


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 Post subject: confused about that Presidium
PostPosted: Wed Sep 09, 2009 10:35 am 
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I am also confused about the new Legal for Trade Presidium scales. Here in Chanthaburi our largest supply store carries an incredible array of balances, but refuses to carry the Presidium line in spite of the fact that he carries almost every other product that Presidium makes. He says they are very problematic. Understand that he carries other balances like Mettler and Sartorius and stands behind them 100%, and even has many Chinese made scales that he says are adequate but not LFT. I bought my Tanita 1230 from him several years ago and it is fabulous and quite accurate, but not LFT.

If you look at Kassoy's website you see that same Presidium scale, and you see that theirs are allegedly calibrated for New York State and other states are a special order item. I think they want $339 for the scale? LOL. I have downloaded and read (and believe I understand) the NTEP Certificate of Conformance for both the 50ct and 100ct models. I have read the owner's manual. It seems that any balance that needs to be "Legal for Trade" needs to conform to Handbook 44- which is the basis of NTEP Class II conformance. The Presidium does. I sincerely doubt that there is any adjustment made that could alter it to conform to Arizona (think Tucson show) that would render it unable to be calibrated for New York, California, or Florida.

If the posters on this thread who know a great deal more about balances and weights and measures bureaucracy than I do can explain how this is possible- and remember you will have to refute the validity of the Handbook 44 tests in order to do so (or at least show that some states will not accept this standard) please do!

As for those of you who sell at shows where weights and measures does the rounds, I wonder this. In order to get my scale licensed in Arizona for the Tucson show I need to supply The make, model, serial number, and NTEP Certificate of Conformance document number. I pay my $14 and they give me my scale license. The same NTEP COC is accepted in Canada also. But are we to believe, as Kassoy and Otto Frei tell us, that they or the manufacturer can do something to make any scale pass the test in one state and not the other when all states use the same C of C? Why would I want the manufacturer (or the retailer, if you would believe that one) to do such a thing? And how can they do it without breaking the calibration seal that this make and model has?

How does a scale know in which state it resides? How does the certificate of conformance know?

Certainly no state in the union (nor Canada) has declared that an NTEP C of C based on Handbook 44 is "just not good enough around these parts"- or have they? I am dying to know the answer.

Also, I have read that in Tucson they don't tell you not to use the scale, they confiscate it. True or false? In Bangkok they just tell you that you can't use it if it is not LFT. I also wonder if indeed weights and measures authorities have the power to confiscate your balance, would they honestly believe that you are selling your stones by the piece?

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PostPosted: Sat Sep 19, 2009 5:39 pm 
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Barbra Voltaire wrote:
True. as long as you are not inferring that the stone you are selling for $X. weighs X.XX carats.. The same is true if you are selling precious metal by weight. Your scale MUST be certified by Weights and Measures.

Of course if you are only using your scale for determinations of SG,etc it doesn't matter....BUT it is certainly a benefit to know that your scale is 100% accurate.
I'm ganna sell my cobalt spinel for 3000. I state the "spinel is $3000." When asked ,"the weight"? I say "maybe 1.7 ct" (safe statement, below actual weight).

Does this reference to weight in this xaction get me into trouble?

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PostPosted: Sat Sep 19, 2009 7:29 pm 
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Ux4 wrote:
Barbra Voltaire wrote:
True. as long as you are not inferring that the stone you are selling for $X. weighs X.XX carats.. The same is true if you are selling precious metal by weight. Your scale MUST be certified by Weights and Measures.

Of course if you are only using your scale for determinations of SG,etc it doesn't matter....BUT it is certainly a benefit to know that your scale is 100% accurate.
I'm ganna sell my cobalt spinel for 3000. I state the "spinel is $3000." When asked ,"the weight"? I say "maybe 1.7 ct" (safe statement, below actual weight).

Does this reference to weight in this xaction get me into trouble?


John, your pulling our leg, right?

You're an Attorney, you know how to write a disclaimer absolving yourself from any indiscretions from minute weight calculations.

Go through e-bay gem descriptions everyday and see how calibrated the scales of the sellers are. Granted these little rocks come from all over the world with different standards for weight calibration and different levels of enforcement, depending on the product.

But, you're not selling pork chops or plutonium that seem to get a little more attention in this country and maybe a little less in others. JTV sells scales by the thousands, scales they claim they use. Who is certifying them for the resale masses?

Here's the disclaimer, "Our scale, (name model # etc) weighed this gem at xxxx on (date and time). I don't think even the big boy labs disclose that information on their reports.

Maybe we should send the same gemstone to several different labs and see how closely their scales are calibrated. Just because they are sanctioned by a higher governing authority, it doesn't mean they're in sync to a universal weights and measures code.

This ain't rocket science folks. The diamond industry would lead you to believe it is.


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PostPosted: Sat Sep 19, 2009 8:55 pm 
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JB wrote:
Ux4 wrote:
Barbra Voltaire wrote:
True. as long as you are not inferring that the stone you are selling for $X. weighs X.XX carats.. The same is true if you are selling precious metal by weight. Your scale MUST be certified by Weights and Measures.

Of course if you are only using your scale for determinations of SG,etc it doesn't matter....BUT it is certainly a benefit to know that your scale is 100% accurate.
I'm ganna sell my cobalt spinel for 3000. I state the "spinel is $3000." When asked ,"the weight"? I say "maybe 1.7 ct" (safe statement, below actual weight).

Does this reference to weight in this xaction get me into trouble?


John, your pulling our leg, right?

You're an Attorney, you know how to write a disclaimer absolving yourself from any indiscretions from minute weight calculations.

even the big boy labs disclose that information on their reports.

LOLz. No me tomo tu pelo! WEll, I wanted to get down with my trade etiquette in case I do offer this stone to one of youz! Yes, I do expect that I would feel very comfortable with the manner in which I consummated the xaction. Thanks for jerking me inline once again JB!!! I needed that! (gud 2 cu).

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 Post subject: Good for Trade Uses in Texas
PostPosted: Tue Oct 06, 2009 4:22 pm 
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Ot used to be that the City Office in Dallas for Weights and Measures would check a scale for accurate weights. There was a rush of hundreds of sellers, so now that certification is provided by repair shops for scales.
Check with your State website for Offices of Weights and measurements for commercial uses. Then check your local city governmental offices.
winstone


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PostPosted: Sat Oct 10, 2009 4:39 pm 
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I own a Tanita 1210 since many years and it has proven to be a very good scale. Recently, a new model of smaller size was produced as the Tanita 1230 which I guess is just as reliable as the old model.
Both have a 20g capacity and a 2mg readability (and one can buy specific gravity kits designed for it from the web).
Tanita is not the cheaper nor the smaller pocket scale around, but I think it's still the very best PORTABLE milligram scale available on the market, by far (this is not only my personal opinion, many people that have been using it say the same)

By the way, I just acquired a new pocket milligram scale (very small sized and very cheap) and will report once I will recieve my 20g class II weight so to calibrate it correctly (which is impossible for the moment as the calibrating weight that was sold with it is of no use). I'm already pretty sure that it's no near as accurate as the Tanita is, but maybe it would still prove to be a worthwhile investment once calibrated, I hope.
What I can already say is that this scale was not that cheap after all, considering that I had to buy a class II weight so to recalibrate it, which costed me as much money as the scale itself!

ps: a few words about pocket scales care.
Avoid exposure to moisture and heat. Keep away from magnets.
Treat it gently: scales are fragile instruments, these don't like shakes and shocks. For that reason, if it's been carried around, always recalibrate before weighing. During weighing, avoid vibrations and air drafts. Don't apply pressure on the weighing tray.


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