How to Clean Leather the Way Conservators Do, Step by Step

A conservator working on the Smithsonian’s Gunboat Philadelphia cleans roughly one square foot an hour. The tools are vacuums, soft dusting, and cotton swabs dipped in an ethanol-and-water mixture. The boat sank at the Battle of Valcour Island in 1776 and was raised from Lake Champlain in 1935, and a previous preservation effort left it coated in liquid nylon that is now aging and peeling, according to WTOP’s report on the project.

Peter Fix, the Texas A&M conservator leading the work, put the logic in a single line: cleaning is “actually a conservation treatment”, because each kind of material on the ship affects it in a different way.

A leather briefcase is a smaller object with the same problem. Dust, a coffee ring, the damp of a train platform and a spore that found a closet in August each do something different to the hide, and the wrong response does more harm than the dirt did. What follows is the order conservators use, adapted for a bag that still goes to work: least intervention first, and stop at the first step that works.

Museum rules are stricter than a working briefcase needs. They still set the sequence.

Step 1: Read the leather before touching it

Hold the bag under a low, angled light and sort what is on it. Loose dust sits on the surface and moves with a brush. Grime sits in seams, creases and around the handle, where hands have been. A pale, chalky film is a different thing again. The Canadian Conservation Institute notes that oils or waxes can leave a white deposit that looks like mould, and its own test uses a mineral-spirits swab on a hidden spot, a conservator’s check and not a kitchen routine.

Fuzzy or powdery growth, or a musty smell, belongs under Step 5. Everything else carries on here.

Pick the test spot now. The underside of the flap or the inside of a strap end shows how the leather reacts before the visible face is involved.

Step 2: Dry-clean first, with a brush

Dry removal comes before any water. The National Park Service’s guidance on leather starts with brushing with a soft brush into a vacuum nozzle, so the dust is carried away and not pushed deeper into the grain. Museum dry cleaning, as described by leathercraft educator Dan Concord, uses vacuuming through gauze, a soft camel hair brush, and sparing use of an artist’s eraser.

Work along the seams and under the edges, where grit collects and cuts at stitching over the years. Keep the motion light.

Dab where possible. Rubbing can move dirt around the surface and create scratches, and a scratched hide is a harder problem than a dusty one. If the leather is flaking or cracked, skip the vacuum: the same source warns that suction can pull loose fibres out. That bag needs a restorer.

Step 3: A damp cloth, then a cleaner only if the cloth fails

Damp is not wet. The University of Georgia’s extension guide to saddle care uses a soft, damp cloth or sponge for routine cleaning, with a clean cloth to take off excess. Museums rarely wet-clean at all, and when they do, the article above describes distilled water on a very soft sponge.

Wring the cloth until it stops dripping. Wipe one section at a time, a panel or a strap, and dry it with a second cloth before moving on. Spots that do not lift on the first pass should not be scrubbed; stop and reassess.

If the cloth fails, the same extension guide calls for a quality leather cleaner on a damp sponge, worked in circular motions and wiped off after. Test it on the hidden spot from Step 1 first, as the International Leather Club article advises. The Park Service adds a caution about solvents: they can dissolve surface deposits but may damage some leathers. The wax finish on bridle leather is part of why the cleaning method matters, and Marcellino NY’s guide to cleaning without stripping the wax covers that side of it.

Step 4: Let it dry slowly

Heat is where a clean bag often gets ruined. The Park Service warns that heat from a hair dryer can drive deposits back into the leather and shrink it. A radiator or a hot windowsill supplies heat the same way, so the same caution applies.

Let the bag air dry at room temperature, away from direct heat. If the shape has slumped, the Canadian Conservation Institute’s approach is to support it with padding such as towelling or foam while it dries. For a briefcase, that means loosely filling the body.

A bag that has been caught in the rain gets the same patience. Marcellino NY’s piece on what rain actually does to a bridle leather briefcase covers that case.

Step 5: Mould is a different job

Mould does not get the damp cloth. The Canadian Conservation Institute’s procedure begins with protection and containment: a respirator, disposable gloves and goggles for small areas, and the object sealed away so spores do not travel. The leather has to be dry before anything else happens. Mould on damp leather smears.

Once the leather is dry, the institute calls for a vacuum with a HEPA filter held close to the surface, two passes, the second at right angles to the first. If the mould smears, stop, because the leather is not dry enough. One warning applies to anyone who freezes or bags a damp item: if left in a sealed bag the mould will grow.

The note gives no wipe-down solution for the leather itself. The diluted bleach in it is for tools and work surfaces, and bleach does not belong on a hide. Spores can remain after cleaning, so gloves and hand washing still apply. Anything more than a small patch is a job for a leather restorer.

Step 6: Decide whether to dress it at all

The last step is the one most people rush. Conservation guidance runs against it: the Park Service concludes that caretakers of leather objects should refrain from dressing leather, because dressings have no long-term preserving effect, can darken and embrittle the hide, and make later repairs harder.

The same publication allows exceptions, including personal objects that have to stay functional, with work boots and baseball gloves as examples. A briefcase carried every day sits closer to the boots than to a museum case. Even so, the case for restraint holds. How often is covered in Marcellino NY’s piece on how often a bridle leather briefcase needs conditioning, and fixing marks that a cleaning missed is covered in scratches, scuffs and water spots on bridle leather.

Questions people ask about cleaning leather

How often should leather be cleaned? The University of Georgia guide suggests wiping off dust and dirt after use and deep cleaning periodically or after heavy use. A bag that sits in a closet needs less than one that rides a commute.

Can household cleaners be used on leather? The sources used here do not support it. The Park Service cautions that solvents may damage some leathers, and the Canadian Conservation Institute reserves bleach for tools and surfaces.

Does cleaning remove patina? Museums often leave marks in place. Dan Concord notes they sometimes record a stain as part of an item’s history, and Marcellino NY’s piece on why patina is a record and not a flaw makes the same case for a working bag.

When is it time to stop? When the next step is stronger than the last, and the last one did not work. Hand the bag to a restorer at that point.

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Sources

• WTOP: Preservationists clean a Revolutionary War gunboat one cotton swab at a time (July 2026)
• Texas A&M Nautical Archaeology Program: The Gunboat Philadelphia Preservation Project
• Canadian Conservation Institute: Removing Mould from Leather, CCI Notes 8/1
• National Park Service: Conserve O Gram 9/1, Leather Dressings
• International Leather Club: Leather Conservation, How Museums Do It (Dan Concord, 2024)
• University of Georgia Extension: The Tack Room, Caring for the English Saddle (January 2025)