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Cas City Forum Hall & CAS-L  |  Special Interests - Groups & Societies  |  Cosie's Corner & Feed Bag (Moderator: Delmonico)  |  Topic: Restoration, Care and Cleaning of Cast Iron Cookware. 0 Members and 1 Guest are viewing this topic. « previous next »
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« on: May 08, 2017, 06:22:19 pm »

After years of practical use, and experiments I have produced this doc I'm willing to share.

Some eye opening info in it.   

Seasoning and Care of Cast Iron Cookware

Seasoning of the cast iron cookware is what makes this type of cookware work so well, yet for the majority it is also totally misunderstood.  What makes the problem worse is so much of the information out there is totally wrong.  Seasoning is not oils that have soaked up into the pores of cast iron like so much of the information out there tells you, it is oils that have been heated up and the volatiles burned out.  This leaves a layer of carbonized/polymerized oils that fill the pores in the cast iron.   

Just like any coating put on a surface, no matter if its paint, plating or seasoning with oil, the surface must be prepared to accept the coating so it will stick. 

Preparing Cast Iron for Seasoning

Just like any coating put on a surface, no matter if its paint, plating or seasoning with oil, the surface must be prepared to accept the coating so it will stick.  Cast iron cookware is no different, no matter if it’s new or used, there are several prep methods, they all work fine and you just need to use what works best for you.

Prepping new cast iron

Most of the new cast iron sold today is what is called pre-seasoned, it is the easiest to work with, wash it with soap and water, dry it, add some oil, get the oil hot, add a couple eggs and then fry them, if it works fine, it is good to go, it is now ready for cleaning and care, if not, the factory did not get it seasoned well, but I’ll tell you how to fix that when we get to the actual seasoning process. 

New but not pre-seasoned will have some sort of oil or wax to prevent it from rusting; often these can be removed with just soap, hot water and a good scrub pad.    I like to take the new piece to be cleaned and put it in the sink, then filling the sink with water as hot as my water heater will put out adding a good squirt of dish soap as it fills.  I then let it soak till the water is cool enough to put my hands in, then I scrub it good with a stainless steel pad and when clean I rinse it then put it on the stove, turning on the burner to dry it.  When it is dry it should have a grey, new iron look, uniform all over the piece, it also may have a little thin layer of powdery rust, this is quite normal and we’ll get to that later. 

Cleaning Used Cast Iron

Used cast iron may or may not need reseasoned; this is something one has to decide for themselves, I tend to clean them up good and look at the old seasoning, if the seasoning is in good shape I just touch it up although to be honest I find few used pieces that really have a good proper seasoning on them, most lack a good base or the base is so thick that it is flaking off.

Now we get to decide the best way to clean and prep used cast iron for seasoning, ask that question in a group of cast iron lovers no matter if it’s an internet group or a group of people in person and you will get a bunch of different answers.  In fact some will almost be militant about their way being the best/only way.   The methods vary, but can be classed as manual, heat, chemical, electrolysis or sometimes a combination of all these methods. 

In our cleaning process we have two goals, one is to remove the old seasoning and the other is to remove any rust, there are several methods that can be used, all will clean your cast iron, one just has to decide which is best for the person doing the cleaning.  I will cover the methods and explain the advantages and disadvantages of each one. 


To me, the easiest is heat because the carbonized oils will burn off at about 700-800F, this temperature range will not hurt cast iron, despite what some people will tell you.   This method will clean all the carbon (seasoning) off the pan, but will do nothing for rust.  Perhaps the easiest heat method is to use a self-cleaning oven if one is available.   A quick explanation of a self-cleaning oven is an oven that will heat up to around 900F, (with in the safe range for the cast iron)  this burns all the carbon off of the oven and any pan in the oven, the oven locks in this mode and can not be opened. 

A caution on using this method is if the piece to be cleaned has a heavy build up on the outside it may be in order to remove this with another method such as a putty knife or a chemical before using the oven, these build ups can often catch fire due to the amount of carbon and oils, not an effect you want in your oven.  Also another disadvantage is you can get a lot of smoke in the kitchen when doing it, although venting and a fan such as a range hood or an open window and a fan will help.

Another method is to use a fire that has burned down to coals, do not use an active fire due to the chance of over heating as well as uneven heating that can warp the piece as well as damage it in other ways. 

I lay the piece or pieces to be cleaned on the bed of coals and add some to the inside to help keep the heat even, perhaps the best time to do this is at night because at around 750F the piece will take on a slight red glow in the dark, this is all you want, if you can see any glow when doing it in the day time the heat is above 950F and you are right at the point of damaging the piece do to softening of the cast iron.   Also you are at the point of getting a red scale (oxide layer) on the piece, this is often called mill scale, but it is not.  Now popular rumor is if you get the red scale, the piece is ruined because it won’t season, the seasoning part is partly true, the scale has to be removed first, but by using 180-220 grit sand paper and sanding to shiny metal it will be fine.  But any piece that has been cleaned by heat needs this done to insure a good seasoning, it’s just it will take more work with the red scaled piece. 

Although the risk is low if done right, I would hesitate to use the heat method on a really valuable 19th century piece due to the fact the metallurgy in these pieces is not as good and internal casting flaws may be there, these are the so called gate marked pieces.  The so called gates are where this older method of casting pours the molten iron.

Gate marked cast iron cookware.
Pictures courtesy of Brad Woods.
When the piece has cooled I take it to the sink and scrub it well with dish soap and a stainless steel scrub pad then I rinse it well and dry it on the stove top with the burner.   I then check to see if all the seasoning has been removed, the bare metal will be a light grey/silver color, the old seasoning will be black. 

If there is still old seasoning left, it can be handled in one of two ways; the first is to put it back in the heat and burn the rest of it off.   If the old seasoning that is left is not real thick and not flaking off I simply sand it smooth and feather it with 180-220 grit sand paper and rinse well and dry on the stovetop again.  One will also often see just a thin layer of powdery rust after drying the piece, this is normal and will be discussed when we get to the point of seasoning the pieces.

Chemical Cleaning of Cast Iron

Chemical methods most often involve either an alkaline substance or an acid substance to remove rust and built up layers, both have advantages and disadvantages.

Alkaline Cleaning of Cast Iron

The alkaline substance most often used in cleaning old cast iron is lye, (sodium hydroxide or potassium hydroxide solution) it is often used in drain cleaners and oven cleaners, and it is caustic so some care has to be used with it.  Lye does a good job of removing the old build up, but is not that good for removing rust so it is better to use it for removing old seasoning and using other methods to clean badly rusted pieces. 

One method often used is to simply buy spray on oven cleaner and to use it on the piece then put it in a garbage bag for several hours or even several days, rinse, scrub well with soap and water and see if all residue has been removed, if not, recoat and let is soak again.   

The other common method involves adding 1 pound of lye to 5 gallons of water (make sure the lye is added to the water and not the water to the lye) and soaking the cast iron in this, the cast iron can stay in it a long period with out harm.   One must remember lye is caustic and one must keep it from contacting the skin and this is best done in an area where children and pets can’t come in contact with it.   When the piece or pieces are done, remove and rinse well in water as per the oven cleaner.

There is some controversy about using lye to clean cast iron, there are some who say that the lye will get down in the pores of the cast iron and not be removable.  Although cast iron has pores, they are not going to soak everything up like a sponge, which is a rumor that floats around.  If one is worried about residue lye, just fill the piece up with water and put a ½ cup or so of vinegar in it and let it soak a while.  If there is left over lye the vinegar will neutralize it and will show it is happening by making small bubbles of Carbon dioxide.  I have never had this happen so I just rinse the piece well, scrub it with dish soap and the stainless steel scrub pad and dry and check the piece as per the heat cleaned one.

Acid Cleaning of Cast Iron

When using the acid method one of three acids are used, one being acetic acid the acid found in vinegar, citric acid found in citric fruits as well as molasses and phosphoric acid, which is often used as metal prep for cleaning new metal before painting but is also used in some soda pop to give it that bite, Coca Cola having what is said to be the highest percent.   

Vinegar can be used straight or diluted, and any type can be used, I use white vinegar because most times it’s cheaper and I use the cheap store brand.  Most vinegar is about 5% acidity no matter the brand.   The method recommended by many for a vinegar bath is a non-metal container big enough for the piece or pieces and fill it with ½ vinegar/1/2 water and submerge the piece in and let it soak for a few hours, remove from the bath scrub as before and resoak if needed.   I myself just use our bath tub since we also have a shower, it is not unusual to have cast iron being cleaned in my tub and it works great. 

The citric acid method most often uses molasses as a cheap source of this acid, the recommended amount being 1 part molasses to 9 parts water, this method is said to take 2-4 weeks by those who use it and the animal supplement type found at farm stores is the cheapest.  I myself have never tried this, but I’m relating it because some seem to like the method, to me it’s too slow. 

The phosphoric acid is perhaps best used as Coca-Cola I have used this in the past as a cleaner for small steel and iron parts, having also used the higher strength metal prep in the past as a painter; I don’t recommend it for home use.   The Coca-Cola works well to remove rust but making a vinegar bath although perhaps slower, is cheaper than the Coca-Cola by far. 

The advantage of the acid method is it does a good job on rust; it is not as good as the alkaline method on old seasoning.   The condition of the piece will tell you which of these methods are best, if not in a hurry use the alkaline method to remove the seasoning and the acid method to remove the rust and by doing the clean-up in that order it will assure people who worry about traces of lye that all of this is removed.

Mechanical Methods of Cleaning Cast Iron

Mechanical can be as simple as a good scrub pad, sand paper, steel wool or other similar items, or it can involve using compressed air to force an abrasive material under pressure, this is called blasting, the abrasive can be sand, steel shot, ground corn cobs or walnut shell or baking soda.   The baking soda uses the finest grit and is what I recommend if having pieces blasted.  The other can leave a very rough surface, depending on the coarseness of the grit, the pressure it’s blasted as well as the skill of the operator using the equipment.   Soda blasting is used for a lot of delicate restoration work so it will be fine on cast iron although it will cost more than the do it yourself methods.   

Electrolysis Method of Cleaning Cast Iron

This method has become popular in recent years, the method uses an electrical currant to remove the rust, it is a process similar to plating with chrome or other metals, but the process is reversed.   The iron from the rust is deposited on another iron rod rather than the metal from a rod being deposited on the piece as in plating; in fact this method is used in restoration work to remove plating before prepping and replating.   

Items needed to do this is a plastic tub big enough to hold the desired amount of cast iron, a non-automatic battery charger, a clean iron/steel rod and some Sodium carbonate (also known as washing soda and available in most grocery stores around the laundry detergent).   

The tub is filled with enough water to cover the cast iron and 1-2 tablespoons of the Sodium carbonate is added per gallon of water.  The rusty cast iron to be cleaned is submerged and the negative lead (black) is connected to the piece/pieces.   The rod is inserted in the solution also, not touching the pieces to be cleaned and the positive (red) lead is connected to it.  The charger is turned on; most sources recommending around 10 amps, this is ran till the rust has moved from the piece being cleaned to the clean rod called a sacrificial rod by the electrons.  The Sodium carbonate is an electrolyte allowing current to flow by lowering the resistance in the water, making it a better conductor. 

This process removes both rust and seasoning; it is perhaps a better method for cleaning lots of cast iron or pieces with heavy rust and carbon build up.  As before, clean the piece with soap, water and a scrub pad, dry with heat and examine to see if you have reached the bare iron, if not put it in the tank and continue till it is down to bare metal. 

Seasoning Cast Iron
No mater what method used to get the cast iron prepped it needed to be seasoned before it can be used.  This is the part where many fail for the simple reason they do not understand what seasoning is.  One of the big problems is there is a lot of bad information out there on seasoning; seasoning is not accomplished by putting some oil on a piece and heating it at just 350F for an hour like many sources state. 

The proper seasoning of a cast iron cooking piece is where a thin coating of oil is carbonized in a process similar to making charcoal, the volatile parts of the oil burn off leaving a polymer carbon coating (long chain molecules) that form a fairly non-stick surface on the top of the bare metal filling the minute pores as well.  Different cooking oils and fats carbonize at different temperatures; this is why the 350F for an hour fails in many cases, the oils/fats are not heated to the carbonation point.   The temperature at where they start this process is called the “smoke point” because the volatile substances in the oils start to burn off creating the smoke.    Different oils and fats have different smoke points and most are above 350F.

The following is a list of some of the common cooking oils and fats listing the smoke point, (sources will show slightly different temps, it depends on the exact composition of the fat/oil which can vary slightly, and this is just a guide with averages).  I really don’t have a favorite for actual seasoning, I normally use sunflower oil (cold pressed) because it is fairly cheap and I use it some in the kitchen, the bottle is easy to grab.

Safflower Oil…………………………510F/265C
Soybean Oil…………………………..450F/230C
Peanut Oil……………………………..450F/230C
Corn Oil………………………………….450F/230C
Sunflower Oil…………………………440F/225C
Beef Tallow…………………………….400F/205C
Canola Oil……………………………….400F/205C
Grapeseed Oil…………………………390F/195C
Vegetable Shortening………………360F/180
Coconut Oil……………………………..350F/175C
Extra-Virgin Olive Oil…………………350F/175C

As one can see some of these are real close to carbonizing at 350F if the oven is truly reaching that temperature although an hour might not be enough time to complete the process.  This is why many end up with a sticky mess or a surface that is not really non-stick.  I will explain how I season cast iron and end up with that durable black surface cast iron needs to have to be truly good cookware.

Let’s address the using to much oils and fats first, I prefer cooking oils which are liquid at room temperature for seasoning, just because they are easier to work with, I take a rag with the oil on it and I wipe and coat the surface to be seasoned with the oil, I then take a clean dry rag (a wad of paper towel will work) and I wipe as much of the oil back off as I can, just leaving a thin film.   With a fat that is solid at room temperature it is best to heat the piece up above the melting point of the fat and wipe as much back off as you can just like the oil, one just has to be careful not to burn yourself in the process.   The secret to seasoning is to not get more than a very thin film on it; any extra is not needed.  I have often seen it recommended turning the piece up-side down and putting a cookie sheet under the piece to catch any drips, but if you have enough that it will drip, you have too much on the surface already.  It is better to remove all you can with the dry rag, it’s ok to do it up-side down, but if it’s on right it won’t drip.

As for the temperature to heat it to, I find that very simple, I turn the oven to the last point before the broiler kicks in and use that setting, it is high enough to carbonize any of our cooking oils but below the point where we will burn the carbon off no matter if the oven thermostat or thermometer is not truly accurate as few are.  I then let the piece/pieces heat in the oven till all smoking has stopped, then turn off the oven and let them cool.  A good vent fan or open windows are needed.  An outside gas grill can be used also, just turn it up to maintain about 500F.

Today there are products on the market made and sold specifically for seasoning cast iron, I have never used any of these, and I have never had any problems seasoning cast iron with the different cooking oils and fats, many of those who have used them claim good results, but I have never had anything less than good results using normal cooking oils and fats, also if you think these products are some sort of magic, think again, they are mostly either soy bean/Canola oil for the liquid ones, or beeswax based for the solid ones with some soy or other oils added.

A quick check shows the liquid ones are about $7-$10 for 8 ounce, the solid is around $10 for 6 ½  ounce cake, that is unless you decide to buy it in the handy container that looks like stick deodorant and then it is $10 for slightly over 2 ½ ounces.   For comparison a bottle of soy bean oil in the liter size can be bought many times for around $1, I find this interesting because no matter what oil you use as we discussed above you end up with carbon, also most instructions that come with these do not recommend heating high enough to fully burn off the volatile substances, this is not seasoning but heated up oils.

Our properly seasoned cast iron is now ready to use, forget these warnings about not using metal utensils “you’ll scrape off the seasoning” if it does you didn’t season it right.  In the next section I will discuss how to clean it and talk about the big myth that goes with cleaning cast iron after cooking.

Cleaning Seasoned Cast Iron after Use

The cleaning of cast iron after use causes a lot of controversy, most is based on the fact many do not get a true carbonized seasoning, as I mentioned above this is the most vital part of getting good results with cast iron. 

The biggest myth says you should not use soap on cast iron because it removes the seasoning, many believe this.  This is confusing to me because if soap and water removed the seasoning when we wash the pieces after use, why do we have to use the above methods when preparing used cast iron for seasoning?   

Ok since that above statement likely has people wondering why you can’t use soap in cast iron, I will say that if your cast iron is seasoned properly then there is no harm, no foul in using soap.  Remember, it won’t get in the pores because we filled and sealed the pores with the seasoning and the real carbonized seasoning won’t come off that easy so why not use soap?   

I can give you reasons to use soap, let’s take the picture below, the remains of a pot roast made with a piece of  beef chuck a fairly fat cut.   As anyone has made pot roast knows this oven is very greasy and washing with plain water will not really clean it that good.  Although true beef tallow will not turn rancid easily, that beef fat has not been properly rendered into tallow and that oven left out in the summer and not used for a couple days risks the beef fat turning rancid.  To prevent the fat turning rancid this oven needs washed with hot water and dish soap, it’s really the sanitary way of doing it.
One problem I run into a lot is most water out of wells in my area is very hard (contains a lot of dissolved minerals).  Of course taking a water softener is out of the question, but there is a solution to this problem.  At most stores in with the laundry detergent you will find a box marked Washing Soda aka Sodium carbonate (yes the same substance used as an electrolyte in the electrolysis method of cleaning).  This is a natural water softener of sorts; it does not remove the minerals but neutralizes the affect of the magnesium and the calcium making the soap more efficient.   It also does a good job of loosening stuck on food on it’s own although since we know soap won’t hurt cast iron properly seasoned there is no reason to not add it also to cast iron with stuck on food.    I’ve found with those hard to clean milk/cheese based dishes I add warm water, a teaspoon or so of washing soda, a bit of dish soap and go on with my work, I get back to it in an hour or so it all wipes out.


Now this is not to say I always wash my cast iron with soap and water, but the reasons I don’t are because I’m in camp, very busy and often with limited hot water.   The below picture is a good example, rye dinner rolls, one can see when removed fully there will be nothing but a few crumbs do to the non-stick nature of cast iron.  At most a quick go over with some water and a rag, or in this case the crumbs will likely be brushed out with a dry rag.   


Another item that will help with clean-up that is often said to remove seasoning is the scrub pads, either the polypropylene type or the stainless steel type.  These being abrasive they could remove seasoning if over used but there should never be a need to scrub that hard with one even if one has burnt something on.   In recent years there has been some “pot scrubbers” marketed that is simply stainless steel chain mail, advertized as not damaging seasoning.  But as we already know any scrub pad is not really going to damage seasoning.  Most I have seen are in the area of $15-20, more than I care to pay, I buy my stainless steel pads at 3 for a $1 at a dollar store and in camp I toss that days one at the end of the day and get a new one for the next day for sanitary reasons and will even toss a dirty one before the end of the day.  At home, I just toss them in the wash with the rest of the dish towels and rags and get months of service out of them.  I’ve tried ones before friends have had, yes they work but are they worth it, that choice is up to you, to me, no.

If one makes a big problem by burning something in a cast iron piece then the best thing to do is to put some water and dish soap in the piece, then bring it to a boil, remove from the heat and let it sit till it’s cool enough to scrub, this has always removed everything from well seasoned cast iron with out harming the seasoning.   

Care of Cast Iron

Once the cast iron is clean no matter what method you use, it needs thoroughly dried to prevent rusting.   The piece can be dried with a towel, but the piece still needs to be heated up to remove all moisture to prevent rusting.  This can be the oven of your stove, a burner on the same or a campfire.  Also in the summer on hot sunny days I just set the pieces out in the sun with the lids off, on a hot day the ovens will often get too hot to touch anyway and using this method saves time and effort, part of my “work smarter not harder” policy.

After the piece is dry it may need to be wiped with a thin coat of oil if the method of washing has removed all the non-carbonized oils.  This is where many think the seasoning has been removed because it doesn’t have that shiny look that is expected, but the gloss is caused by the oils the un-oiled seasoning will be more of a dull black to dark grey.   This is best done while the oven is warm making the oil flow a little better and reach every corner.   Just like seasoning this coat should be very thin, and if possible non-drying oil is best.  Which bring us to another term that need explained. 

Oils Drying versus Non-Drying

Oils are classed as non-drying, semi-drying and drying, some oils will oxidize to the point they will form a dry film.  This is the basis of oil based paints and wood finishes although metallic driers are often added to speed up the process. 

Where to class the oils is determined by an analytical process that determines how much iodine a specific amount of the oil will absorb, no need to get any deeper here, but for our use all we need to know is this is called Iodine Value and number of the iodine value determines where it is classed. 

Iodine values of oils over 130 are considered drying oils and a couple common ones are:
Tung Oil at around 165-175
Linseed/flax seed oil at 135-180

These are true drying oils in their natural state, although Tung oil is not used in cooking, linseed oil is but under its other name, Flax Seed Oil.  When bought as linseed oil or boiled linseed oil it is not intended for human consumption, the boiled has additional products added to speed up drying as mentioned above.   Other common oils ride the line on being drying oils or semi-drying oils depending on the particular lot of oil.  A value of 115 to 130 are considered semi-drying oils.

Semi-Drying Oils

Sunflower at 125-145
Grape seed at 125-145
Walnut at 120-140
Soy Bean at 120-135
Wheat Germ Oil at 115-135
Canola Oil at 110-130
Corn Oil at 110-130

Non-drying oils

Cotton Seed at 100-115
Rice Bran Oil at 100-110
Olive Oil at 80-90
Lard at 60-70
Beef Tallow at 50-60
Palm Oil at 45-60
Palm Kernel Oil at 15-20
Coconut Oil at 5-15

(Values are based on several sources and averaged.)

(Palm Oil and Palm Kernel Oil are different oils from different palms)

To prevent any drying of the oils into a sticky film logic says we should use a non-drying oil. 

I have always preferred olive oil for wiping a piece that will be stored over a couple of weeks, just a thin layer put on with a rag works well, and the excess wiped back off.   For short term I often use lard because it’s there handy and I don’t always carry olive oil in the camp gear.

I see mineral oil recommended at times for both seasoning and preserving cast iron; on the plus side it rates a 0 on the Iodine Value so it has no chance of getting gummy.  But to me the down side is it’s a refined petroleum distillate and although there is a food grade mineral oil it is intended more as a lubricant for food processing machinery, its use in food products is very restricted by law.   One of the medical uses of mineral oil is a laxative and there are many cautions on its uses in that field so I just prefer to stay away from it although some who use it swear by it. 

I hope this helps with some of the mysteries about cast iron, it is really very simple to care for once it is cleaned up and seasoned and only takes a little more care than modern cookware to keep it in shape.


Mongrel Historian

Always get the water for the coffee upstream from the herd.

Ab Ovo Usque ad Mala

The time has passed so quick, the years all run together now.
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