New ideas on tinning

Good Evening All,

Brandon sent me this on tinning process. Hope you find it useful

1st attempt at copper tinning

One of the most common and prolific materials for drinking and cooking vessels during the 18th century was copper. Like tin, it could be shaped rather easily, but with its higher melting point and superior conductivity to heat, it was better choice for somewhat higher temperature cooking vessels. However, one of copper’s drawbacks is that it reacts with acidic foods, causing an oxide to form that is somewhat toxic, especially in quantity.  This oxide leaches into the food and into you as it is consumed. Besides all this it causes the taste to be put off as well.

I don’t know when the practice of tin lining first began, but 18th century tin smiths used the process in their work for their “tin” vessels, which were actually formed from sheet iron. The tin coating, which is non-toxic and does not put off the flavor of acidic foods, effectively eliminates the problem with copper vessels, providing a protective barrier between the copper and the foods, while maintaining the benefits of the copper cookware. All modern copper cookware today is tin lined for this reason.

This brings me to my interest in the subject, for I have well made copper cup which I picked up from a sutler, but it has no tin lining. Since coffee, an acidic drink, is a daily staple of mine, I decided to try my hand at tinning the inside of the cup myself. There are two methods of tinning that I am aware of. The first is hot dipping, in which the whole vessel is dipped into molten tin and is thus wholly lined. The second is a method of hand wiping the tin on the inside of the vessel only, maintaining the appearance and resilience of the copper on the outside. I chose to try this second method, which is much more difficult for the novice but requires less tin. If I were to hot dip my cup, I would need 20-30 pounds of the material at least in order to submerge it.  At nearly $20 per pound, this was not possible for my one time need!

The process begins first by cleaning the surface of the copper to be tinned. I cleaned the inside of my cup well with a modern product called “Bar keepers friend” which both cleans and polishes. The inside of my cup was brought to a shine, and made to look new, unlike the outside which was brown with patina. I next prepared my turkey fryer for the duty of heating the copper, which must be made hot enough to melt the tin and flow over the surface. I first tried using a high temperature heat gun, which nearly worked, but was too slow in the process of heating the copper and keeping it hot enough.

The copper needs some sort of a flux, which prepares the copper to receive the tin and prevents an oxide from forming while it is being heated. My first attempt I used a plumbers paste flux, which did not work well. The solder did not stick. So I had to clean the cup again and start over. I had heard that muriatic acid, the stuff you put in your pool, works as a flux or at least as a way to truly clean the surface of the copper. Since I had some of this already, I tried it. Be careful with acid! I wore safety glasses and a respirator, and of course gloves. I poured some into the cup and heated it over the fryer to boil off some of the water(pool acid is diluted to 50% or so with water). I swirled it around the cup and  finally used my painters brush to brush it evenly all around the inside of the cup. I poured out the remaining acid and returned the cup to the turkey fryer.

The tin I used for this experiment was simply lead free plumbers solder. It is mostly tin with a small amount of silver and copper. I’m told pure tin is best for this process. But this was an experiment and is what I had available. I cut several lengths of tin and put them into the cup to melt with the heat of the turkey fryer. After only moments, they began to flow and I swirled the cup around to spread the solder. This time I could tell it was flowing evenly across the surface, and staying stuck in an even way to the surface of the copper. I soon had to add more, however I could only hold the copper cup for a few seconds before it became too hot to handle, even with heavy gloves.  I removed it from the fire and cooled everything down. At this point I had only covered a few inches of the cup, and even that had many splotches of exposed copper. However, rather than start over, I simply added more acid and repeated my earlier process to clean the surface of the copper.  I added more tin and returned the cup to the fire.

Now I needed to spread the tin up the sides of the cup. For this duty, I needed a dry cloth like denim or heavy linen that would not quickly burn. I wrapped some spare fabric I had around a stick and used this to tilt the cup whilst spreading the tin in a whipping motion. This worked, and spread my meager amounts of tin across the inside surface of the copper. However this rag was not the ideal implement to use as it tended to leave streaks.  I repeatedly had to acid etch the copper, and add more tin until I had coated the whole surface. I got better as I went but the end result when I finally quit was a rather crude lining. However it serves my purpose and I learned several lessons to make it better next time.

Here are the lessons I would use next time. I would be sure to have a holding implement so that I did not have to hold the cup with my gloved hand. Perhaps some special tongs made for the job. I would use a fiberglass insulation wiping stick instead of my rag. This is what the professionals use today as it doesn’t leave streaks, doesn’t burn and doesn’t cool the tin much as it is working. I would also use a torch to apply heat in specific areas. As it was I never got the rivets of the handle to take a coating, probably because I couldn’t get them hot enough. The handle itself acts as a heat sink drawing heat away.

For the sake of learning and doing it myself, this was a fun project that cost about nothing but my time and risk. But consider having your tinsmith do it for you if you are not the adventurous type, or indeed if the quality of the job itself is important! Have a gander at my crude but functional result:


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