Platinum in Laboratory Crucibles, Thermocouples and Industrial Ware

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Last updated: August 13, 2026 · By White Metal Resources Editorial

This page is for readers who found platinum laboratory ware in an inherited box, a university clean-out, a small chemistry business closing down or a home workshop. The sections below cover what these pieces are, how much platinum they hold, how to check that a piece is really platinum, and how a specialist refiner turns them back into metal value. Every figure traces to a primary source cited inline.

Why platinum is used in laboratory ware

Four physical properties explain almost every laboratory use of platinum. The metal is chemically inert to most common reagents, it does not oxidize in air at any temperature, it has a very high melting point and it stays mechanically stable when repeatedly heated and cooled.

Wikipedia summarizes the chemistry in one line: platinum "does not corrode, and bulk platinum does not oxidize in air at any temperature" (source: Wikipedia, Platinum, checked August 2026). It is classified as a noble metal for that reason. It also resists hydrochloric and sulfuric acids, which attack most other common metals used in a laboratory.

The melting point of pure platinum is 2,041.4 kelvin, which equals 1,768.3 degrees Celsius (3,214.9 degrees Fahrenheit), per the same source. That is high enough to hold molten silicate glass, sodium carbonate flux, borate flux and most ceramic melts that a laboratory routinely performs. The metal keeps its shape through hundreds of heat-and-cool cycles.

Wikipedia also cites the specific analytical use: "platinum pans and supports are used in thermogravimetric analysis because of the stringent requirements of chemical inertness upon heating to high temperatures (around 1,000 degrees Celsius)." That single sentence captures why a chemistry laboratory keeps a set of small platinum crucibles on hand instead of substituting cheaper metal.

The trade-off is cost. Platinum is expensive per gram, and lab ware must be shaped by careful metalworking of a metal that is soft when pure. Most cheaper substitutes (porcelain, alumina, zirconia, nickel) work for some of these uses. Nothing else covers the full combination of high melting point plus wide chemical resistance plus mechanical durability under thermal cycling.

Common platinum lab equipment and typical weights

A working laboratory uses a fairly narrow catalog of platinum items. The list below covers the pieces most likely to appear in an inherited or auction lot, with the weight ranges typically seen in retail and used markets.

Weights vary with the manufacturer, the wall thickness and any rhodium alloying. The ranges below are informational rules of thumb, not published specifications.

Sources: Wikipedia entries for Platinum, Crucible and Thermocouple; laboratory equipment product catalogs from Umicore, Heraeus, Johnson Matthey and Alfa Aesar. Weight ranges are informational rules of thumb, not published specifications. Checked August 2026.

The crucible is the workhorse. A 30 milliliter platinum crucible is the standard vessel for silicate fusion in classical geochemistry, where a rock sample is dissolved in molten lithium metaborate at up to 1,050 degrees Celsius before analysis. A laboratory routinely handling this kind of work keeps several crucibles at any time.

The evaporating dish is a shallow open bowl used to boil off solvent from a solution and recover a solid residue. Platinum works here because the residue often contains reactive salts that attack a glass dish over many cycles.

Wire and gauze pieces appear as electrodes in electrochemistry work and as reference contacts in potentiometry. Platinum resistance thermometers are a separate industrial category that uses a specific coiled wire configuration inside a ceramic sheath.

Platinum thermocouples: Type S, R and B explained

Three thermocouple types dominate high-temperature laboratory and industrial furnace measurement, and all three use platinum. Wikipedia describes them in the Thermocouple article (source: Wikipedia, Thermocouple, checked August 2026).

Type S uses a positive leg of 90 percent platinum and 10 percent rhodium alloy, paired with a negative leg of pure platinum. The Type S working range is 0 to 1,600 degrees Celsius.

Type R uses a positive leg of 87 percent platinum and 13 percent rhodium, again paired with pure platinum. Its working range is also 0 to 1,600 degrees Celsius.

Type B uses 70 percent platinum and 30 percent rhodium on the positive leg, paired with 94 percent platinum and 6 percent rhodium on the negative leg. Type B reaches up to 1,800 degrees Celsius.

The three platinum-rhodium types dominate high-temperature measurement because platinum resists oxidation and stays mechanically stable at these temperatures. Base-metal thermocouples like Type K (chromel-alumel) fail earlier because the constituent metals oxidize.

Wikipedia notes that "Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process." Semiconductor crystal growth, ceramic sintering, glass melting and gemstone synthesis all rely on the same set of platinum-rhodium probes.

A finished laboratory thermocouple probe is a small piece of paired wire fused at the measurement tip, threaded through ceramic insulation and enclosed in a protective sheath. Only the pair of thin wires is platinum-bearing. The ceramic parts, the sheath and any connector are not.

Wire diameters run from about 0.1 millimeter for a fine, fast-response probe to about 0.5 millimeter for an industrial probe. Total platinum content per probe is a matter of grams (roughly 1 to 3 grams for a typical laboratory probe), not tens of grams. The Type B probe carries more rhodium than Type S or R and less pure platinum, so its metal value math differs.

How to identify used lab platinum

Three checks together give a strong indication that a piece is platinum. None is a substitute for a professional assay, but the three together will filter out most non-platinum lookalikes before you pay for a refiner's analysis.

1. Read any hallmark or stamp on the piece. Reputable manufacturers stamp their crucibles and dishes with a mark such as "Pt", "100 Pt", "Pt-Rh", "Pt-10Rh", "950 Pt" or a maker mark from Umicore, Heraeus, Johnson Matthey, Engelhard or Sigmund Cohn. Older US pieces may carry "Wilkens-Anderson" or "American Platinum Works" marks. The stamp usually sits on the base or rim.
2. Do a density check. Pure platinum has a density of 21.452 grams per cubic centimeter at 20 degrees Celsius. Weigh the dry piece on a lab scale accurate to 0.01 grams. Suspend it in water on a thin thread and record the apparent weight. Density equals dry weight divided by the difference (dry weight minus wet weight). A pure platinum result lands in the 21.2 to 21.6 range. A Pt-10Rh piece reads about 20.0 to 20.2. A silver, nickel or platinum-plated brass piece reads far lower (silver 10.5, nickel 8.9, brass 8.4).
3. Do a magnet check. Platinum and platinum-rhodium alloys are not ferromagnetic. If the piece attracts a magnet or a magnet clings to it, it is not platinum. Nickel and some stainless steels are magnetic; iron-based imposters fail this test immediately.
4. Look at the surface color. Pure platinum has a silvery-white finish that does not tarnish on the shelf. A yellow tint, a red tint or visible oxide scale is a red flag. A piece that shows tarnish after years in a drawer is not pure platinum.
5. Match the item shape to a laboratory catalog. Lab platinum ware has a distinctive vocabulary of shapes: numbered crucibles with fitted lids, spouted evaporating dishes, notched boats, spatulas with a flat blade at each end. Consumer decorative items in similar shapes rarely appear in this catalog and rarely carry a maker stamp.

The gold standard is still a fire assay performed by a specialist refiner. The five checks above filter out impostors, prevent wasted shipping and let you write a realistic parcel description before sending it out. A written refiner offer, based on their own assay, is what settles the value.

What a used piece is worth: melt value math

Melt value for a laboratory platinum piece is a two-step calculation. Convert the platinum content to troy ounces, then multiply by an example spot price for platinum. Any rhodium content in an alloyed piece is priced separately at the current rhodium reference price.

Spot prices are set on the LBMA twice-daily auction and on NYMEX platinum futures. A refiner does not use a stale spot; the offer references the day the parcel is settled. All numbers below are illustrative computations from a labeled example spot price, not a quote or a prediction of future prices.

The illustrative 916 dollar figure is the theoretical ceiling before any charge. A written refiner offer on the same piece typically lands below that ceiling, because the refiner recovers costs for the assay, the melt, the chemical separation and a small processing loss. Ask two refiners for a written quote before shipping.

Try the melt calculator

Try the same math on your own piece with the calculator block below. Enter a gross gram weight, a share for each precious metal (usually 100 percent platinum on a pure item, or 90 percent Pt and 10 percent Rh on a Pt-10Rh alloy), and a labeled example spot price. The block will compute the pure metal content and the underlying dollar value.

The calculator returns a raw metal ceiling. A real refiner offer sits below that ceiling by the refiner's stated fee schedule. Use the number the calculator returns as your reference when you compare two written refiner offers.

How used lab platinum is refined

Specialist platinum-group-metals refiners take used lab platinum, melt it under controlled conditions, sample the melt for a fire assay and settle the parcel by weight and assayed grade. Only a small number of firms in the United States and Europe run this kind of operation at scale. Sabin Metal, Umicore, Johnson Matthey and Heraeus are the names most commonly cited in laboratory purchasing catalogs.

The refining path for a typical parcel runs through several steps. The parcel arrives, is weighed and photographed. It is melted, cast into a bar and sampled by drilling. The drill sample is dissolved in aqua regia and analyzed by inductively coupled plasma spectroscopy to determine platinum and rhodium content. The assay result and the current reference price drive the settlement math.

Settlement fees vary. Refiners publish either a per-parcel refining fee, a per-troy-ounce refining fee or a paid percentage of the assayed value net of fees. The paid percentage on clean lab platinum sits in a materially higher band than on jewelry or dental scrap, because the material assays higher and processes cleaner.

Rhodium in Pt-Rh alloy pieces is paid separately at the current rhodium reference. Rhodium has traded at several times the platinum price in recent years, based on Johnson Matthey and Heraeus reference series. That makes rhodium content material to the settlement even at low percentages. A 30 gram Pt-10Rh crucible carries only 3 grams of rhodium, but at a reference several times the platinum price, that content is not a rounding item.

Turnaround from arrival to payment typically runs one to four weeks, with faster options at some refiners for a fee. Payment is by check or wire. The refiner returns a written settlement sheet that lists the arrived weight, the assayed platinum and rhodium content, the applied reference prices and the applied fees.

Selling used lab platinum step by step

The steps below cover the practical path from a piece in a drawer to a settled refiner payment. This is a HowTo, not investment guidance.

1. Confirm the piece is really platinum. Read the hallmark, do a density check, do a magnet check and look at the surface. If two of the four checks fail, do not ship the piece as platinum; get it looked at in person first.
2. Weigh the piece on a scale accurate to 0.01 grams. Write down the dry weight. If the piece is likely a Pt-Rh alloy, note the stamp (Pt-5Rh, Pt-10Rh, Pt-30Rh) as an initial share assumption. The refiner assay overrides this later.
3. Request written quotes from two specialist refiners. Ask for the refining fee, the assay fee, the paid percentage of assayed metal, the reference price source they will apply and the expected turnaround. Get the terms in writing before you ship.
4. Ship the parcel insured and tracked. Use registered mail or a specialist precious-metals courier. Include the intake form the refiner supplies. Photograph the piece and the tracking number before it leaves.
5. Wait for the assay and the settlement sheet. Verify the arrived weight matches your recorded weight. Verify the applied reference price matches the day of assay. Ask questions on any line item you do not understand.
6. Accept or dispute the settlement. An assay-based refiner is a repeat institutional business; disputes on clean lots are rare. If the assay is far below your prior estimate, ask for a re-assay or return of the melted bar.

Limits and caveats

Everything above describes the used-lab-platinum path as it stands in August 2026. A few honest caveats belong on a reference page like this one.

• Weight ranges are informational. The 20 to 40 gram range for a 30 milliliter crucible is a rule of thumb, not a published specification. Actual weights depend on wall thickness and manufacturer. Only a lab scale reading is final.
• Illustrative spot prices are examples. The 950 dollar figure used in the worked example is a rounded USGS annual average. A real refiner references the day of settlement. Substitute the current spot to reprice.
• Rhodium and other PGM content shifts the math. A Pt-Rh piece is priced on both metals. The rhodium reference price has moved by a factor of five in a single year in the recent past, per Johnson Matthey and Heraeus reference series. That is normal in a thin PGM market.
• Refiner offers vary. Two refiners can quote materially different paid percentages on the same lot. The difference is fee structure, not honesty. Written quotes are what you compare.
• A platinum-plated or gilt piece is not lab platinum. Some consumer or decorative items are plated with a very thin layer of platinum on a base metal. These pieces fail the density check and are not worth shipping to a refiner.
• Antique laboratory pieces may hold historical or collector interest. A stamped nineteenth-century Achard-tradition crucible or a very early Heraeus piece may sell for more than melt to a laboratory-instrument collector. That path is qualitatively different from a refiner sale and depends on documented provenance.
• Retirement-account rules are a separate topic. Physical laboratory platinum held outside a retirement account is not IRA property; if you are considering platinum inside a self-directed IRA instead, that is covered in our platinum IRA guide, which walks through the IRC 408(m)(3) fineness and storage rules.
• This is not investment or tax advice. A reference page can explain how a used platinum piece is valued and refined. Choosing when to sell, and whether to hold physical PGM at all, is a personal decision that belongs with a licensed advisor familiar with your situation.

Lab platinum questions, answered

Why do laboratories use platinum crucibles instead of ceramic ones?

Platinum crucibles combine four properties that ceramic crucibles do not match together. Platinum is inert to most common reagents, does not oxidize in air at any temperature, melts only at 1,768.3 degrees Celsius and stays mechanically stable through hundreds of heat-and-cool cycles.

Wikipedia notes that platinum pans and supports are used in thermogravimetric analysis because of the strict inertness required at high temperatures. Porcelain and alumina crucibles work in many situations but crack faster under thermal shock and can be attacked by aggressive fluxes.

How much platinum is in a 30 milliliter lab crucible?

A typical 30 milliliter platinum crucible weighs about 20 to 40 grams. The exact mass depends on wall thickness and any rhodium alloying. A pure platinum crucible in that size range holds 20 to 40 grams of platinum. A Pt-5Rh crucible of the same volume holds slightly less platinum (95 percent of mass) and a small amount of rhodium (5 percent of mass). Only a lab scale reading of the specific piece is final.

What is the difference between Type S, Type R and Type B thermocouples?

All three use platinum-rhodium wire and cover high-temperature furnace work. Type S uses 90 percent Pt and 10 percent Rh alloy paired with pure Pt, and works from 0 to 1,600 degrees Celsius.

Type R uses 87 percent Pt and 13 percent Rh paired with pure Pt, over the same 0 to 1,600 degree range. Type B uses 70 percent Pt and 30 percent Rh on one leg paired with 94 percent Pt and 6 percent Rh on the other, and reaches up to 1,800 degrees Celsius. Wikipedia is the source for these compositions and ranges.

Is platinum lab equipment IRA-eligible?

No. Internal Revenue Code section 408(m)(3) requires IRA-eligible platinum to meet a specified fineness (0.9995) and be in the physical possession of an IRS-approved trustee. Used laboratory ware is not held in a depository and is not sold in fineness-stamped bullion form.

If you are considering physical platinum inside a self-directed IRA, our platinum IRA guide walks through the IRC 408(m)(3) fineness and storage rules that apply to bullion coins and bars. Selling used lab platinum for scrap value is a separate, taxable transaction outside any retirement account.

How do I know if a lab crucible is really platinum?

Do three checks together. Read any hallmark or maker stamp on the base or rim (marks like "Pt", "Pt-Rh", "950 Pt" or an Umicore, Heraeus or Johnson Matthey logo are common). Weigh the piece dry and again suspended in water to compute density (pure platinum sits at about 21.4 grams per cubic centimeter).

Try a magnet (platinum and Pt-Rh are not magnetic). If all three checks agree, the piece is very likely platinum. A written refiner assay is what settles the value.

Who buys used platinum lab equipment?

Specialist platinum-group-metals refiners are the primary buyers. Sabin Metal, Umicore, Johnson Matthey and Heraeus are the names most often cited in laboratory purchasing. Each runs a fire assay on the incoming parcel, melts it and settles by weight and assayed grade.

Local coin shops and jewelry buyers will sometimes take small pieces. Their offer typically sits well below what a national refiner would pay directly, because they resell the parcel to a refiner and discount their offer for that margin.

How much of the melt value does a refiner actually pay?

The paid percentage on clean laboratory platinum sits in a materially higher band than on jewelry or dental scrap, because the material assays higher and processes cleaner. Refiners publish either a per-parcel refining fee, a per-troy-ounce refining fee or a paid percentage of the assayed value net of fees. Ask two refiners for a written quote before shipping. Compare on the same parcel weight and the same reference price source, not on headline percentages that can hide fixed handling fees.

Can I refine platinum lab ware at home?

No. Home refining of platinum requires hot aqua regia (a mixture of concentrated nitric and hydrochloric acid), controlled precipitation with ammonium chloride and high-temperature calcination. Every step carries serious chemical and thermal risk, and small errors produce ammonium hexachloroplatinate or platinum salts that can be dangerous to handle. Sending the piece to a licensed refiner is safer, and the assay-based settlement is usually a better economic outcome than a home process would yield.