Some suggestions on how to revive tarnished brass without over-polishing

Summary

This note describes an approach to cleaning old tarnished brass parts of tools without damaging them.

Introduction

Many old tools have brass parts, often set into wood to resist wear, or marked to show a measuring scale. These parts can become badly tarnished if stored in damp sheds, so need to be cleaned as part of the restoration of the whole tool.

However, most collectors agree that it is wrong to polish these parts so they look like a pub's display of horse brasses. Polishing with Brasso or similar

  • would not have been done by the tool's original user;
  • can obscure the pattern of wear (which gives clues about how the tool was used;) and
  • can destroy markings and square edges.

This note illustrates some more cautious techniques.

 Fig01  Fig02

Fig 1 – Neglected mortice gauge

Fig 2 – Another neglected mortice gauge

These are typical examples. Two brass and ebony mortice gauges and a beech brace with a brass chuck.

On all three tools the brass parts need to move freely for the tools to be usable.

 Fig03  Fig04

Fig 3 – Neglected brace

Fig 4 – detail of brace chuck

Cleaning the gauges

Although dirty, the gauges were in good condition and came apart easily.

The first step was just to rub some of the dirt off with the old towel, used dry.

On this gauge I then used a very small amount of Maas brand polish (Maas metal polish cream) on a rag wrapped around my finger. This is a very gentle polish sold for cleaning gold, silver and other metals. If you go slowly and don’t press too hard you can remove just the top layer of dirt but leave the aged appearance. Fig 6 shows what I consider to be as far as I would go. You can see the blackening on the rag.

 Fig05  Fig06

Fig 5 – gauge stem as found

Fig 6 – gauge stem after use of Maas polish

For hard to reach parts – such as around the pins – it was impractical to use rag so I just rubbed gently with a scrap of soft wood. This was enough to remove the surface dirt.

After cleaning I applied a thin coat of Renaissance brand microcrystalline wax to all parts of the gauge including the internal screw thread and sliding parts. This will protect it from handling and prevent future deterioration.

 Fig07  Fig08

Fig 7 – soft wood to clean details

Fig 8 – brass cleaned

With the other gauge, I just used a tiny smear of Renaissance wax on a soft rag and rubbed gently. This is often enough; the solvent in the wax lifts the dirt. It was good enough on the rusty steel screw heads too.
 Fig09  Fig10

Fig 9 – only the right hand side has been cleaned

Fig 10 – slightly more dirt coming off

The finished state – clean enough but not over done.

The wax is also ideal as a lubricant on the moving parts. A toothbrush is good for getting the dirt off.

 Fig11  Fig12

Fig 11 – gauge cleaned with Renaissance wax

Fig 12 – mechanism as found

I used the same wax-only technique on the brass parts of the brace, so as to leave the metal clean but not too shiny.
 Fig13  Fig14

Fig 13 – adjuster after minimal cleaning and lubrication with wax

Fig 14 – finished brace. The brass chuck still shows the pattern of use.

 
 
Cleaning Brass
Ref No: MN 06.01
 
Date: 24-07-2013
 
Author: Andy Tuckwell 
Suggestions for improvement are welcomed, please email: conservation@taths.org.uk
IMPORTANT: The advice in these notes is provided by members and others. It is given in good faith but neither the contributors nor the Society can endorse or guarantee the accuracy or safety of the information. The society does not recommend or guarantee any individual or organisation named.

Treatment techniques described may not be suitable for items of high or historical value. Users should always test first on a small inconspicuous area; observe safety and health guidelines given by suppliers, and dispose of used materials responsibly. The Society does not endorse or guarantee any proprietary products named (and it recognises that other products may be suitable). If in any doubt, expert advice should be obtained

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