Next to wood, leather is one of the most commonly used organic materials in historic objects. It is common to see biological growths or changes to leather in your collection because of the nature of the material, the processing techniques and the care and restoration of leather surfaces. Let’s take a look at what you can do if you see mould.
Why do I have mold?
Mould can be present in the object itself and, in the right conditions, come out of hiding or it can be introduced from airborne mould spores. Most likely the object was stored in a moist dark place which fostered mould growth. Mould grows above 60% relative humidity (buy an affordable gauge from your local garden supplier or a more expensive one from a museum/archival supplier if you’d like to see what your environment is like).
How do I get rid of it?
This will depend on the leather surface:
- Paint/Surface Decoration/Surface Treatment
If there is paint or a surface treatment, you are best to consult a conservator directly. Include photos if you email them so they can get a better understanding of the materials. Solvents may be used to clean the surface, but if you choose the wrong one, you can irrevocably damage the decoration.
- No visible surface treatment
If you do not see any evidence of a painted or treated surface, you may be able to remove the mould yourself carefully (see the supplies list below).
*******Remember to wear gloves (preferably disposable nitrile gloves available at mechanic or medical suppliers) whenever you handle mouldy materials. Also wear a face mask or respirator to prevent yourself from inhaling any spores. Check if those around you are sensitive to mould before using a common area.********
- Tape down some butcher’s paper or other plain paper that doesn’t have a surface treatment onto a work surface. This will allow to see if any mould has fallen off and to clean the work surface easily without contaminating it for other objects or food items.
- Place the object on the work surface being careful to support any areas that are uneven or that could get damaged if pressure is applied. You can use sponges, bubble wrap, pillows or sand bag supports.
- Mechanical Cleaning: (Perform this process in a well ventilated area!!) Use a vaccum with a HEPA filter and micro-attachments to suck up any loose surface mold spores. A great example of how to do this can be found here: Brush Vacuuming for Archival Collections (YouTube). You can use a paint brush in combination with the vacuum attachments for detailed work. Sterilise or disinfect your vacuum attachment set and paint brushes after use. You can also try a soot sponge or museum ‘eraser’ to mechanically clean the surface.
- Chemical cleaning: Mould spores can be reduced from the surface of leather using isopropanol. Test an inconspicuous area of the leather object by dampening a cotton swab slightly with the alcohol. I recommend pouring only a useable portion of alcohol into a seperate container rather than working from the original container to prevent contamination. If you are dipping your cotton swab, you can ‘squeeze’ the excess out by lightly rolling it along your glove on the back of your nitrile covered hand.
- Swab the surface of the leather lightly. You will notice the surface of the leather darken from being wet (there is a small amount of water in the isopropanol sold in pharmacies).
- Allow the surface to dry fully before proceeding. Is the leather permanently stained? Is the tip of the cotton swab very dark? If the swab is only slightly discoloured, you are probably ok to proceed. If the swab is heavily discoloured, there may be a surface treatment such as waxes or oils present and you are best to contact a conservator for treatment.
- If there is no discolouration of the leather or swab, you can proceed with lightly swabbing the surface of the object.
- If you can not swab the surface due to fragility, you may consider misting by using isopropanol in a spray bottle.
- Lightly vacuum the surface again to remove any cotton fibres.
- We do not typically recommend adding any dressing or oils to leather, particularly on objects that are not in use. We also do not recommend placing mouldy materials in the sun as a treatment.
- Discard the butchers paper when done and clean any work surface and tools with isopropanol so you don’t contaminate other objects with mould spores.
Mould can discolour and stain surfaces. You may still see staining from the mould, even if you are positive that the surface was cleaned effectively.
***Please note, this technique does not guarantee that mould spores will not return as this approach may not be aggressive enough to ensure you have gotten all of the mould off, BUT, if you keep the object appropriately stored (see below), you shouldn’t have problems with it regrowing.*****
The treatment you recommended was not successful or there appears to be a surface treatment, what do I do?
Any further cleaning should really be completed by a trained conservator. Other solvents may cause damage, especially on modern or treated leathers. If you are still seeing staining from mould, it may be the case that the discolouration can not be removed. Depending on your circumstances, a conservator may be able to assist in reducing the discolouration.
What is the best way to store an object after treating it with mold?
The best case scenario is to store the object in a cool and dry area that is out of direct sunlight. A climate controlled environment is ideal, although not always possible. Let us know what resources you have to work with and we would be happy to advise on a solution!
What other resources can you suggest on mold?
If you have time, check out these other quick resources relating to mould on leather:
- What is this white stuff?: https://alaskawhitestuffid.wordpress.com
- Mold Overview: http://www.conservation-wiki.com/wiki/Category:Mold/Fungi
- Mold Treatment: http://www.conservation-wiki.com/wiki/BPG_Mold#Conservation_Treatment
- Removing Mould from Leather: https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/removing-mould-leather.html
- Removing Mould from Records and Archives: https://archivesoutside.records.nsw.gov.au/conservation-tip-no-5-removing-mould-from-records-and-archives/
- Plain paper for the work surface
- Masking tape
- Nitrile gloves
- Mask or respirator
- Vacuum with HEPA filter
- Micro-vacuum attachment set (such as those for computer keyboards)
- Paint brush
- Cotton swabs/Q-tips
- Isopropanol (Isopropyl alcohol), available from pharmacies, get the highest percentage that you can