Cosmoline is a grease best known for the use and preservation of firearms by the military, but also serves in many other industries including the automotive and aircraft industries. It was swabbed in as a lubricant to the big guns of battleships and was a grease that tended to just get everywhere as a little bit of sunlight would slowly soften it and a hot deck would melt it. Thus it has a melting point like paraffin wax, but has a much slicker consistency due to other, smaller, hydrocarbon chains. When on metal (and metal coatings) it preserves them, when put on wood it penetrates it to the point you will never get the last of cosmoline out of the wood until you expire... and yet the wood has a lovely preservative that will, on hot days, slowly leech out. Today it is being phased out in favor of thin film coatings that you can apply by air sprayers, but its lubrication and preservation qualities will mean it will be around with our civilization for some time to come.
I have encountered it before as a roughly applied undercoating to vehicles in Buffalo as a final 'winterizing' coat put on during frosty days of December. Particularly in those places that will not heat up, like wheel wells, it can last until the January thaw, that day or two of warm temps that will start to put it through a phase change. Normally it was the cheap auto shops that did that, and they would recommend a different under-coating for the areas that warmed up near the engine and exhaust systems. Getting up close and personal didn't happen until recently, when I purchased a firearm that, while new production, can be modified to fit older equipment, primarily cartridge magazines that were manufactured in truly huge numbers during World War II. So when one can say that they are picking up three magazines from World War II, it does not, automatically, mean that they are picking up printed paper items...
An early warning: if you have never done this before and don't trust some of the cleaners/solvents/methods then try them on a small part *first* and see the results. Wood is its own problem and needs some idea of what you are doing based on what the end product is you are aiming for, as some methods can remove old lacquers and finishes... and some pieces you may want to have refinished and may *want* to get rid of the older ones. Generally the older metal oxide finishes can take a lot more abuse, but if unsure do a small test first and examine the before/after results.
Coming from a background of growing up in semi-rural New York, and having a father who was an electrical engineer and yet had done much else in his life, I knew of some ready cures for things like tar encrustation in engines, oil that had picked up enough junk to look like sludge and other such fun things. And the two methods of getting rid of cosmoline has this under a major heading: Better Living Through Chemistry. The methods my father used are just the same and recommended for well ventilated areas or garages, only: kerosene, turpentine, paint thinner, and gasoline. That and a container for such, normally being a plastic tub that, no matter what it started life as, turned into a grimy black open air pan. That and some hefty toothbrushes that will never be used for anything else and rags, plus maybe a drying rack that may have started life in an oven and now would exist solely for the air drying of metal parts coming from such lovely procedures. Strip down a small engine, drop all the parts into the pan, cover with any of those fluids, and a day later (or even a few hours) you have a pan full of black fluid hiding parts that can now be toothbrushed off and rag dried and put on a rack for air drying, usually in the sunlight.
After trolling through various car and military surplus sites, that way is still a common one for dealing with cosmoline.
For smaller and more delicate parts my father would use such things as WD-40 or a spray on brake cleaning solvent. Those are also popular methods for dealing with cosmoline and require the well ventilated areas, etc. plus rags to help out. Really, if the military surplus stuff was just dunked in a vat of liquid cosmoline for a few minutes or hours, so that it could penetrate everywhere, then you have no idea of if the thing was cleaned before that. Your more aggressive degreasers you will just add toothbrush, rag, elbow grease and rack! Normally you would never, ever let this stuff near a modern firearm, what with all the lovely alloys used, plastics and other things that just might be considered 'junk' by the aggressive cleaners. Stuff from pre-1960 didn't worry about that so much, and most of the common ways of cleaning things in the field would include all sorts of lovely, improvised and often highly toxic and flammable solutions. Beyond those, the other thing to consider is the standard, modern firearms cleaners used to get oil and grease from same which include spray-on oven degreasers, stuff like 'Goof Off' (a personal favorite used to remove sticker residue) and similar items.
Once cleaned you will want to get a nice coating of a modern lubricant/grease on the items (depending on what parts you have), so as to protect them for more regular use. I use KG-3, and it is non-ammonia based and was developed to pour down modern artillery pieces and yet be relatively safe to the user and the environment. I use most of the rest of the cleaning line to support the company, although my pleasure use of firearms is limited when I do use them I want something that is relatively easy to use.
So that is the Better Living Through Chemistry section on cosmoline removal.
Of course, once clean and dry you will want to reapply a modern lubricant and grease to protect the stuff for more normal use. I use Militec lubricant and grease, which I've decanted into smaller containers and applicator syringes for my own use as I've described in other entries.
As cosmoline has a heat based phase change from grease to actual fluid that is the same as paraffin wax, the next method is that of Heat.
If you have taken something apart that has cosmoline on it, put it on a rack over a pan and pour boiling hot water over it. That is, actually, damned simple for small parts, and just requires, like the pure chemical methods, having a pan and rack that you will never, ever use for anything else. Really, if it was just paraffin you could be sure of getting the last of it off by letting it set up, but since it is a grease at normal temps you will instead find that it has spread out over every nook and cranny of the rack and tub and will resist all but the harsh, chemical methods above. Clean, safe, non-toxic and still requires a rag and brush for final cleaning, but you knew that at the start with all of these. Of course since it is a firearm, the last thing you want is water to stay anywhere on the equipment, and so you will soon find yourself putting a lubricant of your choice on the parts.
Next up on the heat area is the EZ Bake Rifle Oven as described in the Surplus Rifle site, in exquisite detail, it is, in essence the equivalent of an EZ Bake Oven, save that you will scale up the concept by using a trashcan. It is simplicity itself to make a low power oven that will heat up to just 140 degrees Fahrenheit with said trash can, lid, light bulb receptacle, racks, drip pans and thermometer. Hell you could probably add a thermocouple and kill switch so that it would automatically turn off when that hot and turn on at, say, 125 degrees. Improvements to it have been suggested, like making it an IR lamp, not a normal light, and so on and on.
Take that idea and scale it down and you get a couple of coffee cans, paint them black, put lids on them and out in the sun, preferably in an enclosed space. For larger pieces, like said entire rifle, you wrap it in rags, cloths, etc. and double wrap it in black, plastic garbage bags and put it in a car for a couple of days when it is all bright and sunny out. Also seen are sheds, attics, racks over wood stoves, cans/containers on top of the furnace in the winter... really an endless array of ways to let passive heating do the job. And if the color of the stuff is generally black, then letting the items sit on a shelf by a window for a few days with rags under them will also do it.
My method started with the coffee container idea, but then went to the other method for dealing with paraffin that my sister showed me: the double boiler. This is, basically, one large outer pot with lots of water heated up until it reaches the melting point of whatever is in the inner pot. I put a second coffee can over the top, used duct tape and floated a small glass with encrusted paraffin in it to find the right temp, and then set it on low. Inside the lower can was my rag of choice at the bottom and I just let hot air do the rest. Necessary for this was a rack on the bottom of the double boiler to keep steam from getting trapped under the can and tipping it over.
A great method described is the use of a hand steam cleaner and a bucket: put rifle over bucket (or other parts) and use the hand steamer on them. For larger pieces you start at the top and work down. You get nice, clean equipment, and still have a hand steamer to get wrinkles out of good clothes!
Also described is kitty litter, black bag or box and sunlight, although I would make sure the kitty litter is clean, unused and then consider the clay residue it can leave... but you will be giving the equipment a good final toothbrush and rag cleaning session, so that might point out spots you missed. Again, Your Mileage May Vary.
No matter what, you will want modern grease/oil/preservative applied to the material, save for wood in case you are going to try and refinish it, then you are on your own, but great articles on that abound.
Finally there is Chemistry and Heat which includes lye soap in hot water, which is sort of the best of both worlds if you don't mind working with lye. Standard degreasers for household use in hot water also have recommendations behind them. I wouldn't want to use the automatic dishwasher method as the cosmoline tends to penetrate when it isn't getting dissolved and really, wouldn't want the taste or smell of that for a few years when doing dishes... if I had an *old* machine used for nothing else set up, maybe.
In theory you should be able to get it cold enough to cake and then just flake off... considering the types of material used in the past, that is probably not recommended. It is the sort of climate like Alaska that plays havoc with this stuff - cold enough to flake off in winter, hot enough to make it run in an enclosed space in the summer.
General rules are:
1) Anything that will be in contact with cosmoline or chemicals will thereafter not serve for any other purpose. A turkey roasting pan will never be used for a turkey or any other roasting thereafter. Rags are for use until thrown away. So empty, used coffee cans are good for cleaning parts, but you won't be storing any consumables for humans in them afterwards.
2) Clean-up of the equipment is still necessary. Who knows where that stuff has been *before* it got dunked and *after*? You don't, that's for sure, unless you are in an old warehouse and find a crate of old WWII surplus equipment or stuff never shipped overseas and forgotten next to the Lost Ark of the Covenant... and there have been some very unhappy surprises of small amounts of moisture trapped by cosmoline and parts rusted out on the inside. Hate to have that happen with other chemicals around industrial and military facilities.
3) Clean-up of you is necessary. Good soap and water, but for some methods a hand cleaner that works on grease and oil, like DL Permatex Blue Label, is necessary. Or gloves... you did make sure that none of the cosmoline or other chemicals spattered or dripped on good clothes, though.... that stuff really does get everywhere when not watched or contained.
4) Ventilation is necessary. Unless you like the smell of cosmoline and cleaners, that is. WD-40 gives me a headache, and really, use of that should be done outdoors. Even the stuff I do use, personally, needs ventilation so it is a positive requirement.
5) Modern lubricants or older ones if no modern equivalent exists. Put on rag, wipe rag over cleaned equipment, use dry rag to wipe afterwards. Use grease sparingly, unless it is recommended by the manufacturer or you can see that it will get some hard use and you won't get back to it very often... then you want one that resists carbon and other deposits and still use it sparingly. My syringes put out so little that the grease often turns into a liquid on contact with metal, because the amount is coming out of a near needle fine opening and metals are a great conductor of heat. Remember to examine for spots you missed, or old worn spots on equipment that may need some greater attention or just recognition that they are worn. Consider lubricants to be a gunk magnet, so they are necessary but used only as needed in as little as needed. Booted CV joints in a car need a lot, your trigger mechanism in a rifle needs extremely little. If you can see it, you probably have too much on unless otherwise specified for the equipment.
Hopefully I will never have to deal with larger equipment... and if you have time, then passive removal of 90% is easy to achieve with patience added in. For me the double boiler and coffee can method worked fine and got rid of the stuff in some very tight places. I used dust-off to get air through those and then a quick hit of KG-3 after. Although those were not active spaces, they weren't ones I wanted drops of cosmoline coming from for the next few years... but I did get some nice special effects on the outside of the can as a few drops of coffee came out from the small space I left uncovered by duct tape. Cosmoline vapors were trapped, coffee sweated out by the drop or three. For that work I got some cheap equipment and a piece of history... and that is without any easy price on it.
My thanks to the soldiers of yesteryear!
That equipment is safe and ready for use, again...