Define "hot-dipped" tin plate

[paulcalloway]

Re: Define "hot-dipped" tin plate

Yes this has been a most profitable discussion. Once Mr. Cunningham has formulated his post we'll look into getting all of this into the articles section.

[P. M. Cunningham, Tinner]

Intermission

Vat just flash fired, so…

The pressure is on now, permanent article status . Hopefully I can keep up the standard. The 201 course has been shifted up to 301 now. I am searching around for the new 201, "19th C. Hot Dipped Technology", that I wrote up years ago on a now dead hard drive. 202 will be simply link material on "The Modern Hot-Rolled System" (I can't write it up better). I may toss in a 203 as a supplement on the "Use of Lead Base Solder"; hopefully, that one is not necessary but maybe good to have up on this forum page.

To respond to some of the previous posts:

Curt's first post:

"...but RATHER our Hobby has come to look at sheet steel that is heated and dipped (or otherwise coated/covered) with tin/lead solder by a number of modern individuals."

Please don't say that anyone is still using lead based solder on liquid food containers!!! This is where the 203 course comes in. I have been trying to push this point for twelve years. FDA regulations for lead are based on using a 10% acid solution on a product, letting it sit for 24 hours and then reading the lead content in the solution. I had product tested by the State lab in Wisconsin on cups soldered with 50/50 tin lead solder with neat seams that pulled levels of lead three times above acceptable levels. If anyone is practicing this system, call your lawyer!!!! This only applies to liquid food consumption (not dry containers for other food stuffs like flour or sugar). I know seven years ago I use to be able to take a lead test kit (yes it was purchased at Wal-Mart) to events and check vendor’s products and got reaction for lead. I really hoped this practice ended.

"And in some circles the uneven coating and sags and runs are held/prized to be more authentic and period. (So what some vendors have been said to do is to take electroplated sheet steel and coat it with solder and call it "Hot Dipped Tinware.")"

And as John stated:

"As Heinrich has pointed out, unless the body of the item appears to be literally "painted" with material, folks simply don't accept it.

Over the years this has been applied and broadened to include canteen bodies, magazines, et., all "period" tin.

I would argue that it is a widely held belief by the Community. Tis a shame we don't have some of the discussions concerning this from a couple years back for your consideration. I used to groan over the cartridge tin magazine discussions of some time ago."

This one feels personal. I wish the discussions were still out there. I lacked the Internet then, so it was only my retailors I discussed this with. I think it was my stuff that defined this argument but that maybe presumptuous. I have no idea what standard was applied by them and spoken by them. Trust me, I will get into this and critique my own process as hard as I do anyone else.

As Michael stated:

"The tin should form a fine sheen on the artifact, not look like dripped candle wax. Is that the correct answer?

Smearing on solder is one thing. I've seen "hot dipped" goods which were (I suspect) "tinned" with aluminized roofing paint."

Yes, you win the prize for the correct answer. Of course you didn't get into the detail, nor was the prize announced. (Forty-gallon trash can of tin scrape work? :) ) This gets into my initial question of what "hot-dipped" tinplate means. I know how my plate could be viewed, but I still lack the concept on what else is out there on the market.

Another branch posted by John:

"...at one point when I was looking into this, some tinned goods that were "improved" or of "extra quality." As I understood this to mean, this was commercially available tinware, that indeed had been made of material specially dipped into a molten vat of zinc or some such, or the material was at least, with a thick layer of paraffin, or animal fats laying on top. I don't know if I could find it again, will give it a shot, and will see what comes of it."

You got right in the animal fat, so you’re not completely "daft". Tin coating in the mid 19th C. involved floating tallow on the top of the tin and having pure vats of tallow. Zinc, however, in a vat is what is commonly referred to as galvanized. The process was developed in the 1850's and was generally used as an architectural material. Zinc does cause a toxin when used as a cooking material but also does provide a stronger protection resistance, which is why it was used for roofing, gutters, cornice....

Jan's comment:

"The pewter in the copper pans..."

Love to know if this is a use of terminology on a continental basis???? Copper is lined with pure tin. Pewter is a tin alloy. 18th and early 19th C. pewter is a lead/tin alloy. Mid 19th C. pewter is an alloy of tin/antimony/bismuth ...(Britannia Ware) . Antimony levels are now being defined as a toxin. What they are and the definition of modern pewter I have not looked into. Copper should be lined with pure tin.

And:

"I know that there are firms here in Germany that custom make hot dipped tin sheet but who could buy a coil with the weigth of over a ton!!!!??"

Actually there was (/is?) a fellow in Canada that got "hot-dipped" plate from Germany. He was reselling it to tinners in the US. Problem was that the coating was a "hot-rolled" process and only had a 1 lb coating. (If you can give me some contact info, I would love to see what they are producing, as long as you can act as a translator.)

Hopefully this clarifies some of the previous posts. It is only my opinion though!!! I appreciate the input, and hopefully more will keep coming. The posts help me define for me what questions/concepts are out there. Keep them coming!!!! I'll get back to the course plan soon.

Patrick Cunningham

[P. M. Cunningham, Tinner]

201, "19th C. Hot Dipped Technology",

Now rain, at least the fire is out.

I have found at least the majority of the article, so back to lesson plan.

“The process of producing tinplate requires a great number of steps which can be divided into two categories: Iron preparation and tinning operation.

The manufacture of sheet iron prior to the 18th century was by hand hammering. This process was labor intensive and kept the manufacture of tinplate to relatively small levels. In 1728 the introduction of rolling mills allowed the iron sheets to be formed by the hot pack method. This process involved passing hot iron between rollers to make it thinner, folding the metal over on itself, and repeating the process until the desired thickness was achieved. This process was used until the 1920’s, when cold reduction process of forming sheet steel began to be used.

After the sheets had been formed the next step was to descale them, which was sometimes referred to as “black pickling”. They are immersed in a leaden vat filled with muriactic acid and allowed to steep four or five minutes. From here they are taken into a reverberatory furnace where they are left until the heavy scale falls off and they become annealed. They are then run through cold rolling mills to polish the surface of the sheet. The material may at this stage go through a second annealing at a lower temperature to remove the hardness put in by the rolling mills.

The next step is “white pickling” which removes the final film of oxidation, which developed during the cold rolling and annealing. The sheets are put in vats of lye for ten to twelve hours, then transferred to vats of sulfuric acid for about an hour, from which they emerge clean and ready to plate. The sheets are then placed in vats of fresh water to prevent surface oxidation until they are plated. These processes can be seen in the illustration from Diderot on the first tinplating plate.

The actual tinning process took place in multiple vats, and although not every manufacturer used the same procedures, the steps involved remained basically the same from the 18th century through the 19th century. The cleaned sheets were removed from the fresh water vat and immersed in a vat full of burnt grease, which served as a flux to prepare the iron for bonding with the tin. Once coated they would then be immersed in up to three successive vats of tin to build up a layer of tin on the steel, each vat containing more pure tin than the last. These vats contain a mixture of block tin and grain tin, grain tin having fewer contaminants of iron, sulfur, and other foreign substances. Each of these vats would have from two to six inches of grease floating on the top of the tin to prevent oxidation of the tin. The grease would be a mixture of linseed oil and suet, tallow, or palm oil depending on the time period. The vat temperature would be kept just below the flash point of the grease being used, about 500-600 degrees Fahrenheit, with each vat being slightly cooler than the last one.

Once the tin was on the sheet any excess tin was removed, leaving a smooth surface. This was done by a process called washing. This process involved five stages; a tin-pot, a wash-pot with a partition, a grease pot, a draining pan, and a listing pot. The wash –pot contained pure grain tin and had a partition it to keep the dross from the previous tin vats from contaminating the entire surface of the vat. This partition was an early 19th century improvement. Because sheets placed in the tin pots would be dipped in the wash-pot, the wash-pot would slowly pick up impurities and be transferred to the less pure tin pots from time to time.

Directly after being removed from the tin pots the sheets would be dipped in the wash pot on one side of the partition. Upon being removed the sheet would be wiped on both sides with a hemp brush to remove the excess tin. The sheet would then immediately be dipped into the other side of the wash pot and quickly removed to erase the brush marks.

From here the sheet would be dipped into the grease pot to smooth out the last irregularities of the coating thickness. Once removed the sheet would be placed on the pan to drain and cool. When cool, the sheet edge would be dipped in the listing pot, a shallow pot of tin about ¼” deep, designed to melt only the drip edge that had built up through the previous steps. When removed from the listing pot the sheet would be hit sharply on the edge with a piece of wood to shake off the excess tin. This would leave the sheet with a faint stripe at the bottom edge which could be seen on every sheet of tinplate sold.”

Patrick Cunningham