Wednesday, 28 November 2012

Roundhouse Objects Conservation - Nov. 27, 2012

November 27, 2012

Metal Objects Cleaning

Metal objects are challenging to clean.  There are several examples as part of the railway roundhouse collection that I can prepare for long term storage and display.  Two of them at least at first appear particularly difficult but in the end are not so hard to do.  In this post I will show you how this can be done.  There are two steps to this process: 1) cleaning and 2) preventive maintenance.  I will concentrate on the cleaning in this post and discuss the second step in a later post.  The metal objects all have some corrosion products (rust) in various degrees.  When I say difficult I mean that they are heavily corroded.  Why clean them at all?  It is to reveal any markings such as makers marks, copyright marks, registration numbers and so on.  All of which will help us to date them and determine how they were made and used.

Keep in mind that I will avoid the use of chemicals in the cleaning process and prefer to use mechanical means.  Therefore, the tools I use in cleaning these are as follows:
  • brushes: usually a toothbrush with stiff bristles for removing dust and smaller material,
  • picks: usually toothpicks and shish-kabob sticks for scraping (to avoid scratching),
  • scalpel: usually used to pry off loose material

Padlock - before cleaning
Padlock - after cleaning, closeup

The object on the left is a padlock used by the railroad. We know from other examples in much better shape that there is usually embossed lettering on the key hole cover which runs vertically down the centre of the main body of the lock. It is obscured and unreadable in the photograph on the left. By using a scalpel I was able to carefully remove large chunks of corrosion material to reveal the marking as shown on the right in a close-up photograph. I used the toothbrush to remove dust and other smaller, loose material to make the lettering even more visible. The embossed letters "CPR" vertically down the key hole cover can clearly be seen.

Canadian Pacific Railway (CPR) on November 13, 1911 leased the operations of the Dominion Atlantic Railway (DAR, incorporated on October 1, 1894) effectively taking ownership, although DAR maintained its own identity for most of its existence.  Therefore we can date this padlock to sometime after 1911.  Eventually all (or most) padlocks with the letters DAR were replaced with CPR lettering.  There is also a registration number on the back of the hasp (not shown here).

The photograph below shows the material removed, the tools used (toothpicks and shish-kabob stick not shown), and the end result - a cleaned up padlock.

Conservation Tips: Be very careful when using sharp tools such as a scalpel (besides the ever present safety issue) by keeping in mind that it is very easy to scratch the metal object.  I carefully used the scalpel to pry material loose not to scrape it.  That is, I insert the sharp edge in cracks and pry it up, leveraging the blunt edge.  The photograph above shows several very large pieces that came loose.  Certainly, it is more time consuming to do it this way but I find that a combination of prying carefully followed by brushing with the toothbrush works best and alternating this back and forth as many times as needed for the desired result. The wooden picks can be used for scraping but again, be careful.  In this example, the corrosion was generally very loose and relatively easy to remove.  Consult a conservator to determine how far to go with the removal of corrosion who will remind you that scratches may result if you go too far.  The next step is to coat the object with museum grade wax to prevent further corrosion by sealing it off from contact with moisture.

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