Dirty Insulator

Cleaning Your Insulators

Compiled by Bob StahrView Icon Profile, Ian MackyView Icon Profile and Bill MeierView Icon Profile

Acid or Base?

There are many different ways to clean insulators. For just plain dirt you can just wash it off with soap and water with a scouring pad or SOS pads. If you use a scouring pad be sure that it says it is safe for glass; some can leave fine scratches on the glass. For sticker residue, a solvent like Goof Off (xylene) works well. But the problem for most people is usually train smoke, that gray haze or black coating that covers all, or part of, the insulator, particularly the underside where it's not regularly washed clean by rain.

If the insulator has a dull etched look, or other stains that don't come off from cleaning, you may want to read the section about Tumbling Insulators for more information.

There are two basic cleaning choices for train smoke, soot, tar, paint and the like: acid or base. Either can be used to effectively clean glass and porcelain insulators. The most popular cleaner is oxalic acid due to its availability, cheapness, safeness and excellent cleaning ability. The most popular base is sodium hydroxide, known as lye. It's more dangerous, but will remove some deposits the acid won't touch and is safe for carnival glass (unlike an acid solution).


Do not use oxalic acid to clean carnival glass, flashed amber, or use it on soft glass such as the Hemingray E-14B's and D-510's in opalescent milkglass. The Mexican CD 133.5 Tel Fed Mex seems to be made of very soft glass, and is affected by oxalic acid. The acid will take any coatings off an insulator including carnival and flashed amber. I have heard of stories of the soil eating the E-14B's away to nothing so I imagine the acid would do the same; don't try it!

The lye solution is safe for cleaning carnival glass and flashed amber pieces.

Oxalic Acid

Oxalic acid is a white crystalline powder commonly called wood bleach. It can be bought at local hardware or supply stores; look for 100% oxalic acid crystals with no additives.

When mixed properly, it produces a weak acid solution that is fairly safe for skin and fabric yet will strip most foreign materials off an insulator in a single day.

You may already be familiar with this substance as the common weed Yellow Oxalis, know to many a kid as sour grass, has a high concentration of oxalic acid in the flower stalks. Chew on them and get a super-tart, sour taste -- the taste of oxalic acid.

Preparing the Acid Solution

Mix about a 1 pound of acid with every 2 1/2 gallons of water. Using hot water will help to dissolve the crystals faster, but remember to let it cool down before placing your insulators in the bath.

Remember to always add acid to water. An old high school chemistry saying goes like this: do like you oughta, add acid to water. The dust of oxalic acid can be dangerous if inhaled and a dust mask is recommended during this part of the procedure. Safety gloves and goggles are recommended during handling of chemicals.

5 gallon plastic buckets are recommended for the acid bath. Be sure you always use a plastic bucket, not a metal one, as the acid will eat metal! Please make sure you put a lid on it so no small children or pets will fall in or play with your insulators, and it's a good idea to label the lid as to its acid content.

This weak acid solution is relatively safe to work with. You can use bare hands to remove and replace insulators from the bath with no ill effects, though any open cuts or abrasions will sting. Just be sure to rinse your hands off in water within a minute or two.

A particularly dirty insulator make take two or three days in the bath, but if the deposit's not coming off by then the acid will probably never remove it. You may want to try sodium hydroxide.

After being used, the acid solution will become dirtier and dirtier, darker and darker. But the cleaning power of the acid is not diminished, so resist the temptation to throw out the bath and start over. The acid bath can be used for hundreds of insulators. If the water level drops over time, just add more water to bring it back up.

Sodium Hydroxide (Lye)

Sodium hydroxide, commonly called lye, is a strong base that will do as good a job as oxalic acid for general cleaning, but will also remove some deposits the acid won't.

Lye can be bought at most grocery or hardware stores. On the West Coast, the common commercial brand is Red Devil. Again, look for 100% sodium hydroxide with no additives

The main danger in using a base instead of an acid is that where an acid will burn the skin and cause pain when it's contacted, a base will painlessly dissolve the skin, so it's possible to suffer a worse burn before realizing what's happening. In addition, sodium hydroxide is not readily diluted with water and therefore not easy to flush out of your eyes.

If you do get a base on your skin it will dissolve into a slippery slurry of skin cells. That is the main characteristic of a base: it makes your skin feel feel slippery. If you're wearing rubber gloves, the insulators will not feel slippery and are no more difficult to work with than with the acid bath.

The particular advantage of lye over acid is that it will remove some things that acid will not. In particular, the heavy varnish-like deposits in the pinhole will come loose with a day or two of soaking.

Like the acid bath, the lye bath will become darker with time as it is used, but it will remain effective for hundreds of insulators. The solution will eventually become pitch black, but it will keep on working.

Preparing the Lye Solution

Mix about 12oz (one Red Devil can) of lye with every 2 gallons of COLD water. Do not use hot water or the mixture will emit dangerous fumes and possibly splash. Do not put the lye into the empty bucket and then and add water to it; instead, fill the bucket halfway with cold water and then add the lye. Safety gloves and goggles are always recommended during handling of strong chemicals.

When you first add the lye to the water the solution will heat up and emit a vapor. Avoid breathing the vapor! In addition, be sure to wait until the solution has cooled to room temperature before soaking your insulators.

5 gallon plastic buckets are best for the lye bath. A plastic bucket is safest as lye attacks a number of materials (wood, paint, some metals, etc) but not the plastic used in common 5 gallon paint buckets. Of special note, lye violently attacks aluminum so do NOT use an aluminum container and do not stir the mixture with an aluminum utensil. A long stainless steel or plastic spoon is recommended for stirring.

Please make sure you put a lid on it so no small children or pets will fall in or play with your insulators, and it's a good idea to label the bucket as to its dangerous lye content.

Preparing the Insulators

The first thing you need to do is bring the insulator to room temperature. A significant temperature difference can crack an insulator. This is why you should never use a dishwasher to clean insulators.

Bringing an insulator in from a cold, unheated garage and putting it under hot water will probably crack it. You should clean off all the loose dirt and debris from the insulators. Neither acid nor base does a good job on sticker residue, so remove this first with a solvent. This will keep your solution lasting longer.

Cleaning the Insulators

Generally after a day in the bath the paint, tar, or soot should come off easily. However, you can soak the insulators for several days for stubborn deposits. If you can find a 1" diameter round brush it is helpful for cleaning the pinholes of insulators, as does a toothbrush.

The scouring pads or SOS pads work well for taking out some of the stubborn spots and getting in between the petticoats. Take care to also scrub around the embossing and the drip points! A stiff brush is useful for this too. Again, be sure the temperature of the bath and the rinse water are the same, to avoid thermal shock and the potential for cracking.

Pieces that are sandblasted or frosted from burial can not be cleaned with this acid treatment. This will not restore their luster. There are occasional instances in which the glass will not come completely clean and will have a hazed look. Sometimes these insulators can be tumbled with a mild buffing compound to restore the luster. Several insulator people and a number of bottle people provide this service. The section Tumbling Insulators tells about this process in more detail.


The authors are not responsible for failure to follow these directions, misuse of, or any accidents with, the cleaning solutions presented here, or any damage to your insulators.

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Last updated Tuesday, August 27, 2013