Nada como «brujulear» por internet buscando formas de verificar nuestros metales preciosos en forma de monedas. Lo primero, aquí os dejo unas gráficas al respecto…

https://www.burbuja.info/inmobiliaria/threads/evolucion-del-precio-del-oro-vi.1029048/page-133

Me encuentro con argumentos interesantes en diversos foros

«…Lo de los lingotes de China ocurre por la misma razón que todavía algunas mujeres, con la cantidad de avances que hay, se quedan preñadas sin quererlo, NO SE PONE EL DEBIDO CUIDADO.

Se nota que muchos foreros no se han leído el hilo al completo porque hay asuntos más que aclarados y explicados, en mi caso creo que he posteado en el foro un par de veces esta info, esta será la tercera si no me equivoco.

Me refiero al riesgo de ser estafado, que de hecho existe, pero que con un poco de cuidado y una mínima inversión se puede esquivar sin problema a los demonios metaleros que rondan por ahí.

En monedas es fácil, te aprendes las medidas de diámetro, grosor, peso y aleación y no hay mas. Es imposible fabricar una moneda de otro material diferente al oro o la plata manteniendo las mismas medidas que una original.

Existe una excepción, el Wolframio o Tungsteno, que tiene el mismo peso específico que el oro, pero que no es fácil utilizar en el caso de monedas pequeñas.

Para evitar este potencial riesgo de que te den Wolframio por liebre, existe un aparatito cuya eficiencia he podido comprobar empíricamente y que no requiere excesiva inversión en su compra en comparación a las ventajas que ofrece.

Se trata de un medidor de ultrasonidos:

EDELMETALL AURO PRÜFER GOLD PLATIN PALLADIUM SILBER LEGIERUNG TEST PRÜFSET SD9 | eBay

Funcionamiento:

– Se aplica una gota de fluido para ecografias sobre la pieza en cuestión, (también vale lubricante DurexPlay, je..je…)

– Se configura la velocidad en el aparato de ultrasonidos (Oro=3240 m/s – Plata=3650 m/s) estas medidas cambiarán en el caso de aleaciones, pero eso ya es cuestión de investigar un poquito.

– Se realiza la medición que ha de coincidir con la medida que obtengas con un pie de rey o calibre.

Como el tungsteno tiene una velocidad sónica más elevada (5400 m/s) que el oro, en el caso de una falsificación, aunque las medidas y peso coincidan, la prueba de ultrasonidos será infalible y delatará su falsedad dando una medida totalmente diferente al calibre.

Un detalle, no vale para piezas muy delgadas (de 1/2 onzas para abajo) pero si para onzas enteras y cualquier tipo de lingote…»

https://top-messtechnik.com/Edelmetall-Auro-Pruefer-SD9

Source: Fischer Instruments

Otros aparatitos con el mismo principio físico: ultrasonidos

https://www.pce-instruments.com/english/?action=Query&-query.&query.katalog.key=40043&query.stichwort=td+40+gold&query.mode=OR

https://www.olympus-ims.com/en/applications/ut-testing-gold-bars/

https://www.measurementshop.co.uk/blog/product-focus/sauter-td-gold-ultrasonic-gold-tester-overview

Detalles en otro foro

«…My GM100 arrived today. That’s was fast shipping since I ordered from a seller in the USA. It came in a soft mailer and inside was an outer cardboard box and inner fitted metal case holding the unit. Batteries included (3 AAA’s) The instruction manual is a paper copy of the manual that can be found online. Not much there except the basics and a chart near the back of velocities to use for various materials including gold and silver. More or less plug in the transducer and turn the unit on. Transducer is 10mm in diameter. Since there’s two identical transducer leads and they aren’t marked, I assumed it didn’t matter which when where and I plugged them in and turned it on. It ran a self-test and ended up with a velocity setting of 5900 m/sec. 

It comes with a 4mm standard to test measure and is used for calibration. After putting a bit of the silicone goop on the test standard it measured 4.0 – 4.1 mm each time I checked it. I then tested a 10 oz silver bar which was handy and it measured way too thick. So I changed the velocity setting to 3600 m/sec as suggested in the materials chart and got a reading of 6.3 – 6.4 mm which varied depending upon area tested. That was about correct using an eyeball thickness of the bar using a handy ruler. The bar has a flat back, but has a statue of liberty face on the front side that varies in height. I then tried a nickel clad copper core US quarter to see if it measured the correct thickness. I got 1.8 mm (1.95 mm is correct) using the copper velocity setting and so it does suggest it could tell plated fakes. 

So upon first testing it seems to respond to selected metals when changing velocity and does repeat itself. 

It will require more time to do full sample testing and use of a micrometer or dial caliper for more exact test results of some PM. I don’t own any known fakes and really don’t want to own any and so my results may not meet your needs. 

I am willing to test known fakes if someone is willing to send a couple to me and I will return them to their USA owners – however, I don’t want international packages with stuff that could lead to legal issues…»

https://gold-forum.kitco.com/showthread.php?149220-Need-assistance-finding-a-decent-Ultrasonic-Thickness-Gauge-for-gold-verification

Pequeña introducción al tema de conductividad eléctrica

https://www.silverbullion.com.sg/Articles/Detail/A-new-addition-to-testing—Electrical-Conduc/960

1.     Testing electrical conductivity is perfect for authenticating silver

Because silver is the most conductive element in existence, no other metals can be used to fake silver. Even if people try to mix and match metals and substances to form different alloys, it will be impossible to match the conductivity of silver because alloying a pure metal will cause its conductivity to decrease. In short, it is theoretically and practically IMPOSSIBLE to have a metal or an alloy to match the electrical conductivity of silver!

For gold, it might be theoretically to mix and match metals to obtain an alloy to match the electrical conductivity of gold, but it would not be possible to have an alloy that matches both the electrical conductivity AND the density of gold. Therefore, measuring the electrical conductivity as well as the density of the bullion is a truly definitive non-destructive test to authenticate pure gold.

2.       Tolerances are up to 16 times stricter than compared to ultrasonics

In-house statistical studies have shown that the tolerances obtained from electrical conductivity measurements are up to 16 times tighter compared to readings obtained from ultrasonic measurements. This makes our testing methodology much more reliable and sensitive (see point 3 on sensitivity).

3.       Gold and silver are extremely sensitive to impurities

A presence of small amounts of impurities can greatly affect the electrical conductivity of gold and silver. For example, from the chart below, we can see that the electrical conductivity of pure gold is at 45 MS/m. Ducat is a gold coin with 1.6% copper impurity. As seen from the chart, a mere 1.6% of impurity lowers its electrical conductivity to 25.3 MS/m. That’s more than a 40% reduction in electrical conductivity.

Aquí  https://www.sigmametalytics.com/  midiendo conductividad eléctrica; el aparato es más caro

Y de postre…