Laboratory Tube Cleaning

In glassware, the residue sits where a brush reaches last. Precipitate settles into the round bottom of a test tube. A pellet sticks in the point of a centrifuge tube. Film runs the full length of a burette or pipette bore. Residue in a flask collects in the shoulder that the neck hides.

Each of those needs a different head: a tufted end for a round bottom, a tapered tip for a cone, a long fine brush for a narrow bore, a fan or bottle-form head that opens out past a neck. A brush that does not reach the residue leaves it for the next experiment.

The glass adds two rules. A bare wire tip can crack or punch through the bottom of a tube, and scratches on graduated glass spoil the reading. So the wire end is always covered and the fill is soft enough for glass.

Sizes from the laboratory brushes we make:

Size the head from the inside diameter of the glass: near-size to wipe, 5–20% oversize when the nylon has to scrub. Test tube brushes always get a tufted end. For flasks, a fan-shaped or bottle-form trim spreads past the neck and reaches the shoulder; for cylinders, a stiffer stem stops the brush bowing against the wall.

Burette brushes are long, up to 1,000 mm to order, with an optional 10–20 mm end tuft. Petri dishes take a flat round brush, 60, 90 or 100–120 mm, with a metal-free build where needed.

Galvanized cores are cheapest and fine for water and detergent; choose 304 or 316 stainless as soon as acids are involved. Tell us the solvents in use as well: strong solvents attack some fills.

• Rinse out loose residue first, then fill the glass with warm detergent solution.
• Push test tube brushes down until the tuft touches the bottom; turn gently, without stabbing.
• Push burette and pipette brushes straight through; do not spin them against the graduations.
• Rinse with tap water, then with purified water as your procedure requires.
• Dry brushes hanging, and replace any brush whose wire end shows through the fill.

• The glassware: types, inside diameters and depths, or a list of the sizes in your range.
• End shape for each: tufted, fan, bottle-form, cylindrical or sponge.
• Fill and core, with the detergents, acids and temperatures in use.
• Single brushes or graded sets, and packing and labeling.
• Quantity per size; the minimum for small brushes is 500 pieces.

Grease and organic films that brushing does not shift need a soak in a laboratory detergent or the cleaning bath your lab uses. Some residues, such as dried protein or silicone grease, need a specific solvent or treatment first. Volumetric glassware for accurate work is often cleaned without brushing at all, to keep its calibration.

• A test tube brush with a worn tip, whose bare wire end cracks or punches the bottom.
• Spinning a brush inside graduated glass until the marks are scratched.
• Galvanized cores in acid baths, which rust and leave iron in the glass.
• One brush for every size, too loose for small tubes and too tight for large ones.
• Putting brushes away wet in a drawer.