There is a common assumption that cleaning ends when the object is clean. In fact, at that moment you have returned the metal to roughly the state it was in the day it entered the ground: exposed, reactive and ready to corrode all over again.
Preservation is not a final polish, it is the mandatory last step. Before you start it, make sure the cleaning is genuinely finished: copper and bronze, iron and cast iron. If the object has only just come out of the ground and cleaning has not happened yet, this is not where you begin — start with the first 24 hours after a find: a barrier over an undried, undocumented object is not preservation.
Rule zero: dryness
Everything else is secondary. Wax on a damp object seals the moisture in. You have just built a small airtight chamber in which corrosion will be extremely comfortable.
- After chemistry, rinse with distilled water, thoroughly.
- Dry with warm air. Porous iron needs days, not hours.
- Don't seal anything that is still damp or still shedding.
If green powder or orange spots come back, that is not a reason to apply thicker wax. It is a reason to go back to treatment. More often than not the cause is not the barrier but salts and moisture left inside the object — see water, salts and hydrolysis.
Wax or paraffin
One barrier does not suit every object
Wax, oil and an acrylic consolidant are different answers for different materials and different states, not three brands of the same thing. Dense bronze, porous iron, thin gilding or silver plating, enamel, glass, bone, leather and any composite object all behave differently under a barrier: what is a thin protective film on one is sealed-in moisture, or an irreversibly altered surface, on another.
Before you apply anything, answer three questions: what the object is made of, what exactly sits on its surface, and whether that layer can be removed later without harm. If even one answer is missing, no barrier goes on — the object goes into dry, stable storage and observation instead, and, if anything is actively changing, to the advice in special cases.
| Product | Pros | Cons |
|---|---|---|
| Microcrystalline wax (e.g. Renaissance Wax) | Thin, controllable film; museum practice for small objects | Costs more, wants a light hand |
| Paraffin | Cheap, quick barrier for field finds | Easy to overdo and end up with a crust |
Either way: apply thinly and wipe the excess with a soft cloth. A thick layer does not protect better — it just stops you noticing that something is happening underneath it.
BTA, briefly
Benzotriazole is used as an inhibitor for copper and its alloys, in hobby practice too. The usual approach is a solution in alcohol, a short soak, drying, then wax. Be more careful on silver, where the appearance can change.
What matters is what it is not: BTA does not cure active bronze disease and does not replace sesquicarbonate.
Oil for iron
Clean dry iron gets a thin film of neutral oil or a dedicated product, with the excess wiped off. For larger pieces oil is often more practical than wax — easier to apply evenly and easier to renew. Storage still has to be dry. See also special cases.
Paraloid B72
A museum acrylic consolidant, mixed with solvent to a recipe. At home it is only worth it if you understand what you are doing with concentration and ventilation: get it wrong and you have a cloudy film to remove.
For most everyday finds, wax or oil plus dry storage gets the same result with noticeably fewer ways to miss.
Storage is preservation
The layer of wax decides less than the conditions the object sits in for the other 364 days of the year.
- A dry place at a stable temperature. Silica gel in the box helps.
- Don't stack dissimilar metals against each other in a damp environment.
- Look at them once a month. New spots mean drying and re-sealing.
- The cleaning date and the product used need to be written down somewhere. The find card is also a good place for an "after consolidation" photo — in a year you'll have something to compare against.
A conservation log, not memory
A year from now you will not remember which product is on that buckle, when it went on, or whether the box was ever moved. Memory is not a record; a conservation log is. One card per object, filled in as you go, is worth more than any extra coat of barrier.
| Field | What to record |
|---|---|
| Initial state | Photos before any intervention and a description of the surface as found |
| Material and confidence | "Copper/bronze?" beats false precision |
| Intervention | Date, who did it, the aim, the materials and actions used |
| Storage conditions | Place, packing, moves, any noticeable change in the environment |
| Monitoring | Inspection date, reference photo, changes or the absence of them |
| Escalation | When and to whom the object was shown, and what limits were advised |
The log is not about archival tidiness. It answers one practical question: has anything changed since last time — and if so, after what exactly. How to set up a regular inspection rhythm, and what counts as a change at all, is covered in conservation monitoring.
If the changes come back
A return of bloom, powdering, cracks, a tacky film or flaking is not a signal to repeat the previous method "harder". First compare the object against the reference photo, check the storage environment, and read back through the earlier treatments.
- Compare with the reference photo: is the change genuinely new, or was it always like that.
- Check storage: humidity, packing, dissimilar metals side by side, the state of the silica gel.
- Read the log: does the onset coincide with a new product, a repack, or the box being moved.
- Record the observation with a date and a fresh photo — before the next attempt, not after.
If the change is active — the powdery area is spreading, salts are surfacing again, plating is lifting — the route leads not to the next method but to assessment and advice: special cases. Running the same treatment again without understanding the cause usually costs the object a little more surface and settles nothing.
What not to do
Wax over active bronze disease or wet iron is not preservation, it is a way of temporarily not seeing the problem. Thick paraffin applied "forever", after which nobody inspects the piece, works the same way.
And separately: don't put freshly cleaned metal into a plastic bag undried. Condensation inside the bag will undo the whole job in a fortnight.
In short
- Cleaning finished, spots stable.
- Distilled rinse, then a full dry.
- Barrier chosen for the material and the state, not "the usual one".
- Dry storage, date and product written into the log.
- A check-up a few weeks later, changes go into the log.
External orientation
Preservation is mostly about storage conditions, not a coat of wax. What museums actually control — humidity, packing, regular inspection — is described at Canadian Conservation Institute — Metals.