Silvering vs. Tinning

[Matt Lukes]

I'm just curious: does anyone actually have any provable evidence that Roman stuff was ever actually coated in tin, or is the common use of 'tinned' is simply a misnomer like the use of 'bronze' for any copper alloy is?

I have a handful of pieces in my personal collection that are 'tinned' and when I tested the coating metal with a tiny drop of chlorine bleach, I got a gray/black spot indicating the metal is actually probably silver- tin oxidizes white, not black so it's clearly not tin.

[mcbishop]

I'm just curious: does anyone actually have any provable evidence that Roman stuff was ever actually coated in tin, or is the common use of 'tinned' is simply a misnomer like the use of 'bronze' for any copper alloy is?

There are published analyses that prove the use of tinning (dipping in a molten tin alloy) on items (there are references in B&C2 IIRC but I can't check at the moment). What confuses the issue is that silvering (the application of thin silver foil) was often secured using a lead/tin solder with a very similar composition to the coating used in tinning... further complicated by the fact that some items (the saddle plates from Castleford spring to mind) were both tinned and silvered (silvered over the visible surfaces, but tinned beneath the separately attached bosses)!

Tinning tends to be pre-Flavian, silvering Flavian and later, but that is a rule of thumb and not written in blood... or molten tin.

Mike Bishop

[Matt Lukes]

Thanks Mike- that answers the question perfectly. It just struck me as rather surprising that every one of the coated pieces I have- acquired from various sources over more than a year-and-a-half or longer- just happened all to seem to be silvered and none tinned.

One piece does appear to have leaf on it, but most others look rather the way things coated using modern tinning flux do- the layer is very thin and melted-on. Clearly purified silver wouldn't work since it's melting temperature is higher than that of brass or bronze, but if alloyed with lead, it might be significantly lower and be rather more like our silver-bearing solder.

[MARCvSVIBIvSMAvRINvS]

So, if some things were tinned.... would they have used (proper) tin? or a lead based alloy?

since you often read about the dangers of lead-poisoning, zould this also have anything to do with the inside of their patera and other pots and pans?

M.VIB.M.

[Nerva]

Most Roman 'tin' contained lead, it makes it very easy to work. It's not possible to give exact content. Leaded tin is generally referred to as pewter, although modern pewter contains no lead.

Tin is an element and is extracted from it's ore, cassiterite which is tin oxide SnO2. One of the greatest properties of tin is that is easily forms alloys. This is also one of its problems. So in Roman tin you fine everything from Lead, Bizmuth, Iron to zinc mixed up with it.

Don't forget, you only have to go back 100 years to find Lead pipes, sinks and drains. In fact, in some parts of this gread island Lead pipes are still in use

[Celer]

Salve,

In fact, lead pipes do not create lead-contaminated water. Lead quickly forms a stable white oxide on the surfaces that come into contact with water (such as the inside of a pipe), and this prevents any further erosion or dissolving of lead. Increased levels of lead were apparently found in Roman era teeth (an article on New Scientist, I no longer have it) but the source of lead was more likely to have been pollution arising from silver mining!

Vale,

Celer.

[Matt Lukes]

Quite so- our modern 'fear' of lead is, like many things, a little overblown- sure it's not nice stuff, but tiny amounts aren't going to kill you, and may only affect you over long periods of exposure time.

Acids are the main culprit for getting lead into food and drink- the members of the Franklin Expidition to map the Northwest Passage in Canada's nort, for example, are thought to have suffered from significant poisoning as a result of contaminated acidic canned foods- the acid acting on the lead solder that sealed the cans. Of course this was over a period of years with the men eating only the canned food and perhaps occasionally seal meat. And the lead poisoning didn't kill them- disease, exposure, and starvation did- it is just suggested to have seriously affected their mental processes such that they made questionable decisions and were ultimately all lost.

[MARCvSVIBIvSMAvRINvS]

ah okay! didnt know that!! very interesting!!

TY!!

M.VIB.M.

[Memmia]

Quite so- our modern 'fear' of lead is, like many things, a little overblown- sure it's not nice stuff, but tiny amounts aren't going to kill you, and may only affect you over long periods of exposure time.

Acids are the main culprit for getting lead into food and drink- the members of the Franklin Expidition to map the Northwest Passage in Canada's nort, for example, are thought to have suffered from significant poisoning as a result of contaminated acidic canned foods- the acid acting on the lead solder that sealed the cans. Of course this was over a period of years with the men eating only the canned food and perhaps occasionally seal meat. And the lead poisoning didn't kill them- disease, exposure, and starvation did- it is just suggested to have seriously affected their mental processes such that they made questionable decisions and were ultimately all lost.

Hi, I saw a great TV reconstruction of this a few years back. It showed how the crew under the influence of lead poisoning trying to salvage heavy relatively useless items like writing desks and empty crates instead of valuable resources. They tried to drag these with them over the ice! This waste of energy from very poor judgement and mania did indeed contribute to their deaths in the end from malnutrition and exposure. The blue line on the gums which is a symptom of lead poisoning was still visible when the frozen corpses were discovered perfectly preserved many years later.

P.S.Re silvering: Here's a handy housewife's tip :wink: - Oxidised silver can be brought back to a great shine using dilute ammonia solution. Test a small piece first though.

[Matt Lukes]

Exactly. While enough lead can kill you directly, generally it just messes you up- causes anaemia, harms your immune system, organ, nerve and mental functions. I just read that it's suggested to be the causitive agent in the supposedly prevalent gout suffered by the Roman upper class- no reference was given, but it seems plausible.

Lead acts the way many toxins do by interfering with normal cellular enzyme activity- it inhibits a few important ones thus decreasing or halting functions that have reaching effects. The most important one is the enzyme that is involved in making a basic component of hemoglobin- the oxygen-carrier of blood cells. Decrease the oxygen around and everything suffers- hence some of the multisystem and more long-term effects of lead poisoning. Also the body can't effectively dispose of lead so it accumulates and its effects continue and worsen over time if the exposure continues.

[Nerva]

While it's fair to say that the risk of poisoning from lead pipes is relatively low, there is a significant risk associated with the use of lead lined vessels such as sinks, cups and bowls. This comes from the fact that the surfaces of such objects are regularly scored and scoured as part of both the eating and cleaning process.

However, there is no evidence that the Romans used such vessels, they used tin alloys instead. The lead levels in the pewters or tins of the time were relatively low. It would have taken a determined attempt over a long time to get lead poising from these sources.

The only real way to ingest any harmful level of lead from such sources would be through melting the surface alloy. Now this is very plausible. You have to be very careful when using tin or pewter coated utensils such as frying pans etc, as the low melting point of the alloy lends itself to easy melting and so contamination of the food.

[Matt Lukes]

The only real way to ingest any harmful level of lead from such sources would be through melting the surface alloy.

Well while melting certainly could be an issue given that an average campfire (just dry wood) can be as hot as 500-600C (or more) and both lead and tin melt well below that, it's hardly the only way to get harmful levels of lead since the majority of lead poisioning is a long term thing, not one of large dose ingestion. Just as was the case with the solder of the tin cans, acidic food, especially when heated, will cause the release of lead ions from a lead-tin alloy coating on a vessel even if there's no melting. And it's certainly the case that the constant abrasion of utensils and cleaning would keep a 'clean' metal surface that is most easily attacked chemically by those agents that would ionize the metals.

I could see the issue of melting coatings being an obvious one to anyone using the vessels such that they'd know how to use them properly- i.e., without melting the coating, if for no other reasons that it'd contaminate the food and damage the protection the coating gives. Imagine eating food with little particles of metal in it? Doesn't sound terribly apetizing :lol:

[Nerva]

We use tinned frying pans. The last time we tried to use them we put it over far too hot a flame and the bloody coating started to melt. I hope it's lead free...