Cast Iron Cookware Myths & Misconceptions

While resources like this website and others have endeavored to inform and educate about the history and proper treatment of vintage collectible cast iron hollow ware, there is still much misinformation being proliferated, both online and in the marketplace. Presented here, in no particular order, are the top ten most-often encountered examples.

Belief #1: Cast iron cookware is virtually indestructable.
True or False?: False. Cast iron is durable, but not unbreakable. Like glass, the properties that make cast iron hard also make it brittle. Cast iron subjected to impact or twisting force will break before it bends. Heating an empty pan or a large pan over a small burner too quickly may also result in cracking or irreversible warping.
Origins: Most likely confusion between cast iron and wrought iron or steel.

Belief #2: The best, easiest way to clean build up from a cast iron pan is to burn it off in a fire.
True or False?: False. While fire will indeed typically completely remove build up, intense heat will often damage the pan, either by warping or cracking it, or by potentially altering the molecular structure of the iron, making it irreversibly scaly.
Origins: Most likely from frontier era camp cooks who would have had no other way to refurbish heavily encrusted pans.

Belief #3: The coating of seasoning on a pan imparts flavor to cooked food.
True or False?: False. The term "seasoning", as it pertains to cast iron cookware, applies to the build up over time of polymerized and carbonized cooking fats, resulting in a corrosion-resistant, non-stick coating, and has nothing to do with food seasoning. In this case, the meaning is akin to calling an experienced person a "seasoned veteran" or properly dried firewood "seasoned". Traditional cleaning methods should leave no residue which would affect the taste of subsequently prepared foods, although oily fish might be an undesirable exception.
Origins: Uncertain. The claim is often heard from sellers of used, unrefurbished pans, more than likely in a misguided attempt to make thickly encrusted pieces seem more valuable.

Belief #4: The large numeral seen on the bottom of a pan or the top of a pan handle indicates its diameter in inches.
True or False?: False. The numerals were an early convention used to denote what size woodstove eye a pan fit. Sizes were not necessarily consistent across all brands, so one maker's #8 pan may not have fit another maker's #8 stove eye. The numbering system continued to be used for some time even after the advent of gas and electric cooktops.
Origins: An erroneous assumption made by those unfamiliar with early woodstoves.

Belief #5: Small letters inscribed on cast iron pans indicate the manufacturer.
True or False?: False. Small individual letters seen inscribed in cast iron pieces are pattern identifiers. Multiple patterns were used to create the molds for several pieces at once, so some way of keeping track of which unique pattern made which piece was necessary, either for quality control or piecework payment. Similarly, small raised letters on pan bottoms are typically molder's marks, stamped into the sand mold just prior to casting by a foundryman in order to keep track of his daily production.
Origins: Another case of misinformed sellers trying to increase the value of otherwise unmarked pieces, for example any letter "G" seen claimed to be "code" for Griswold.

Belief #6: The "old iron" ore mined and used to make cast iron cookware around the turn of the century (early 1900s) was superior to that used later in the 20th century.
True or False?: False. Elemental iron does not exist in nature in its pure form. While variations in composition exist between iron ore obtained from different sources, the smelting process used to extract the elemental iron from the ore would have removed most if not all undesirable impurities. The iron used to create cast iron is not used "as smelted", but rather ingredients such as carbon and silicon are added to give the metal desired properties. And, while earlier foundries may well have used solely virgin iron ore, any reclaimed scrap which may have been added by domestic manufacturers later in the 20th century was held to purity standards and tested before use.
Origins: Older cast iron cookware was hand poured using more finely-grained sand molds to which finish-improving treatments were applied. Manual mold creation also allowed the production of thinner-walled, lighter castings. Coupled with the now-discontinued practice of polishing cooking surfaces smooth, the older processes resulted in a more finely cast and finished product. The term "old iron" being used to convey superiority is therefore more applicable to the cookware itself rather than to the metal from which it was made.

Belief #7: A cracked pan can be detected by listening to the sound produced by tapping it.
True or False?: True, but with exceptions. The saying goes, "Rings like a bell when tapped with a wooden spoon." An intact pan does typically make a definite ringing sound when tapped while being hung or held in a certain way. The same pan with a crack tends to produce a dull or less-distinct ringing sound. The technique is virtually useless, however, when trying to assess an encrusted pan, the build up both obscuring visual inspection and suppressing sound vibrations. Thicker, heavier pans also tend not to produce as noticeable a ring as thinner, lighter ones. Being a subjective test at best, it should not be relied upon in lieu of a close visual inspection of a clean pan under adequate lighting.
Origins: Uncertain. The observation was perhaps made often enough to establish the rubric.

Belief #8: Miniature cookware was made to be given away as salesmen's samples.
True or False?: False. The tiny vintage cast iron and aluminum cookware pieces manufactured by the major name brands and others were produced as children's toys. Made in most cases to the same standard as full-sized cookware, they were intended for actual cooking as well as play. Often sold in boxed sets, catalogs of the era as well as the marked containers confirm the original purpose.
Origins: While some toy cookware may have been given away to business clients, the misconception may have roots in the miniaturized demonstration units created to lighten the load of traveling stove salesmen.

Belief #9: Cast iron is revered for its even heating ability.
True or False?: It depends on how you define "even heating". If you believe that the heat applied by a burner will spread evenly throughout the pan, then the answer is "false". Cast iron is actually a relatively poor heat conductor, which means that the area of a pan to which heat is applied will increase in temperature but with diminishing effect as you measure further away from that area. Its density, however, allows it to store more heat per pound relative to other metals.
Origins: Confusion likely exists between iron's ability to store heat vs. the ability to heat uniformly. Its low conductivity makes it slow to heat up, but, once hot, it stays hot longer, serving to eliminate sudden temperature spikes. In that sense, iron does more readily maintain an evenness of temperature. The best way to evenly pre-heat a cast iron pan is in the oven.

Belief #10: Washing a cast iron pan with soap will ruin the seasoning.
True or False?: False, in most cases. A well-seasoned pan will be armored with a reasonably tough, near-plastic layer of polymerized cooking fat and carbon, capable of withstanding cooking temperatures of several hundred degrees. Although normally unnecessary, washing with warm water and regular dishwashing liquid using a non-abrasive pad or scrubber will not materially affect a well-established seasoning. Cast iron pans should not be left submerged in water, however, and certainly should never be put through an automatic dishwasher cycle, regardless of how well-seasoned they are.
Origins: The prevalence of lye, or wood ash pre-20th Century, as a soap-making ingredient is a possibility. The boiling of lye (sodium hydroxide) or wood ash (to produce potassium hydroxide) with animal fat in cast iron pots to create soap was found to remove the seasoning. The culprit, however was not the soap, but the alkali used in making it. A very basic initial seasoning in which the fat or oil used is incompletely polymerized, however, may well be affected by vigorous scrubbing with dish soap.

Belief #10½: Acidic foods should never be cooked in cast iron pans.
True or False?: Both. While it is true acidic foods will cause iron to leach into them, a well-established seasoning layer will provide a barrier between the acidity and the iron. The same may not be true, however, of newly seasoned pans.
Origins: A pan with insufficiently-established seasoning can indeed impart iron to or react with the foods cooked in it, especially acidic foods like tomatoes, or liquids like wine, vinegar, etc. This may result in a metallic taste to the food or even a discoloration of foods like beans or spinach.

Honorable Mention

There are a few other misconceptions you will encounter from time to time, including:

That the markings on cast iron pans are stamped into them.
Cast iron, at least that used for cookware, is not malleable enough to be imprinted upon by stamping. The markings may have been stamped into the pattern (usually made of aluminum), but they were cast into the pan. The same is true of hammered finish cast iron pieces.

That cast iron is porous.
Many have been led to believe that not only is cast iron porous, but that those pores expand and contract with changes in temperature, allowing oil or other foreign substances to not only adhere but to be "absorbed" or "sealed" into the iron. While even polished iron is not completely flat, any voids are simply microscopic irregularities resulting from the removal of crystalline graphite, a carbon component of the cast iron, at the surface.

That cooking in cast iron is a valuable source of dietary iron.
Once a pan is well seasoned, the polymerized oil/carbon coating forms a barrier between the food being cooked and the iron. If one were to cook food, especially food with an abundance of moisture or acidity, in an unseasoned pan, however, there would be a transfer of iron to the food. Cooking in an unseasoned cast iron pan is not normally done. (Individuals with hemochromatosis, an iron overloading disorder, should probably avoid food cooked in any cast iron, nonetheless.)

That, after using and washing, a cast iron pan must be immediately re-seasoned.
Washing with non abrasive pads and common household dishwashing liquid will not remove the coating of polymerized fat and carbon that comprises the seasoning of a cast iron pan. There should be no reason, therefore, to apply and bake on another manual application of oil after each use.

That the color of rust on a reproduction item is different from that of a genuine one.
Rust is rust. Ferric Oxide. Hydrated iron oxide or iron(III) oxide, chemical formula Fe2O3. The differences in the color of rust relate to how advanced a state it has reached on a particular piece or the level of moisture it contains.

That a reusable "mold" is used to make cast iron pieces.
Cast iron pieces are made in divisible molds consisting of a mixture of moist fine sand and other compounds which is packed tightly around a reusable pattern. When the mold hardens, its halves are separated, the pattern is removed, the mold is reassembled, and molten iron is poured into it. When the iron cools and solidifies, breaking the sand mold away from the piece effectively destroys it.

That skillets marked "ERIE" were made by a predecessor to Griswold Mfg. Co.
The too-often seen term "pre-Griswold" used in reference to Erie skillets is a misnomer. Griswold made them, first under the auspices of the Selden & Griswold Mfg. Co. and then the Griswold Mfg. Co.

That flaxseed oil is superior to other oils or fats as seasoning.
It Depends.
Many new collectors find an online blog article expounding the virtues of flaxseed oil as having scientific basis for superiority as a seasoning fat. Although the results are cosmetically impressive, many have found that, in use, the manually applied coating tends to flake off. It may be worth noting that flaxseed oil is not typically used for heated cooking. And since you will not be cooking with it, the seasoning you do build by cooking will be some other fat or oil applied on top of it.