What Is a Clay Triangle?

A clay triangle is the small ceramic-and-wire triangle that supports a crucible over a burner flame. It is one of the oldest pieces of equipment still in daily use in a chemistry lab, and it is also one of the most frequently misunderstood, because at a glance it looks like it does the same job as a wire gauze. It does not. This page covers what a clay triangle is, what it is used for, how to size one to your crucible, and how to use it without cracking it.

What Is a Clay Triangle?

A clay triangle is a length of steel wire bent into an equilateral triangle, with three short ceramic tubes threaded onto the sides. The wire ends are twisted together to form legs. The ceramic tubes are made from pipe clay, which is where the tool gets its other names: pipeclay triangle, pipe clay triangle and pipestem triangle all refer to the same thing.

The triangle sits inside an iron ring clamped to a ring stand. A crucible drops into the opening at the centre and rests on the three ceramic sides, held above the burner with nothing between the flame and the base of the vessel.

What Is a Clay Triangle Used For?

The clay triangle exists to hold a small vessel directly in a flame at high temperature. Its main uses are:

  • Supporting a crucible during ignition or ashing, where a sample is heated strongly enough to burn off organic material or drive off water of crystallisation.
  • Holding an evaporating dish while a solution is taken to dryness.
  • Gravimetric analysis, where a precipitate is heated to constant mass in a crucible and the mass difference is the measurement.
  • Any procedure that needs heat higher than a water bath or hot plate can supply and a vessel too small or too round-bottomed to stand on a gauze.

The shape is the whole point. Three narrow contact lines hold a conical or round-based vessel steady while leaving almost the entire base exposed to the flame. A flat support would either not hold a crucible at all or would shield its base from the heat.

Why Pipe Clay and Not Bare Wire

Bare steel wire held in the hottest part of a laboratory burner flame will scale, soften and eventually sag under the weight of a loaded crucible. It will also transfer contamination onto the outside of the vessel, which matters in gravimetric work where you are weighing the crucible itself.

The pipe clay tubes solve both problems. Fired ceramic keeps its strength far above the temperature a Bunsen or Meker burner reaches, and it is chemically inert against the vessel. The steel wire underneath never sees the flame directly because the ceramic sleeve takes the heat. If you want the temperatures involved, our guide to how hot a Bunsen burner flame gets covers the range and why published figures vary so widely.

What Size Clay Triangle Do You Need?

Clay triangles are sold by the length of the pipe stems, typically 1.5, 2.0, 2.5 and 3.0 inches. That measurement sets the size of the opening at the centre, and the opening is what has to match your crucible.

The rule is straightforward. The crucible must sit in the triangle so that roughly the upper third of the vessel stands above the ceramic. Too small a triangle and the crucible perches on the very top, unstable and easy to tip when you touch it with tongs. Too large a triangle and the crucible drops through, or sits so low that its rim is level with the ceramic and you cannot get tongs around it.

If you run a mix of vessel sizes, two triangles will cover almost everything. A 2.0 inch for crucibles and a 3.0 inch for dishes is the usual pair.

Clay Triangle vs Wire Gauze

These are not substitutes for one another, and choosing wrongly is the most common mistake with both.

  • A wire gauze is a flat square of mesh that sits on the ring and spreads the flame into diffuse heat under a flat-bottomed vessel. Use it for beakers and conical flasks, where a concentrated flame on a single spot would crack the glass.
  • A clay triangle holds a round or conical vessel in the flame with the base exposed. Use it for crucibles and evaporating dishes, where you want maximum heat and the vessel is fired ceramic or metal, not glass.

Put simply: glassware goes on gauze, crucibles go in a triangle.

How to Use a Clay Triangle Safely

  1. Clamp an iron ring to the ring stand at the height you want, then set the triangle inside the ring with its legs resting on the ring. Do not clamp the triangle itself.
  2. Seat the crucible before you light the burner, and check it is stable by nudging it gently with tongs rather than a finger.
  3. Position the burner so the tip of the inner blue cone sits just under the base of the crucible. That is the hottest point of the flame, and holding the vessel higher wastes heat rather than protecting it.
  4. Move the crucible only with crucible tongs, and only by the sides, never the rim. Never lift the triangle itself while anything on it is hot.
  5. Let the assembly cool on the ring stand. Transferring a hot crucible to a cold bench top is how both crucibles and bench surfaces get destroyed.

Care and Common Failures

Pipe clay is brittle and it does not like sudden temperature change. The two failures you will see are a cracked or crumbled ceramic sleeve, usually from a splash of cold water onto a hot triangle, and a distorted or sagging wire frame, usually from the sleeves having already failed and left the wire exposed to the flame. Neither is repairable and both are safety issues, since a triangle that has lost a sleeve can drop a red-hot crucible.

Inspect before every use. If a sleeve is cracked all the way through, slides freely on the wire, or is missing, retire the triangle. They are inexpensive enough that there is no argument for keeping a damaged one in service. Store them flat in a drawer rather than stacked in a beaker, where the sleeves knock together and chip.

Shop Clay Triangles and Crucibles

Avogadro's Lab Supply carries the full range of pipe stem clay triangles, together with the crucibles and tongs that go with them:

More reference material is in our Lab Reference Guides.