Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
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| Examples of Precolumbian Tumbaga Artifacts. Obtained by simple google search using keywords Precolumbian tumbaga. |
It isn't always easy to identify items found on a beach or shipwreck. Without considerable experience, a lot of mistakes can be made. Way back when I started I know that failed to recognize many items.
When you think of treasure you might think of pictures of pirate chests over-flowing with sparkling gold. You've seen the pictures in the movies and fiction books. On the other hand, if you think of things that are centuries old, you might expect them to look old. In both cases, you might be wrong.
Years ago I didn't know that gold was enameled back in the 18th century. When I saw a nice gold enameled ring, I quickly and wrongly concluded it was modern. I was wrong.
One thing you might easily misidentify is tumbaga. It can look like gold even though it can be anywhere from three percent to ninety-seven percent made of alloys such as copper and silver.
The Precolumbian natives encountered by the conquistadors knew how to work metals. They used alloys and gilding.
Many items that looked like gold even were actually of a much lower purity.
A phenomenon often encountered when ancient objects made of noble metal alloys are analyzed is that of their surface enrichment. Let us consider, for instance, a statuette made of an alloy of gold with copper and/or silver; it can occur that its surface has a percentage of gold higher than that of the bulk. This enrichment can be due to an addition of gold on the surface, or to a depletion process during which the less chemically stable elements leach out causing the surface composition to change. In both cases, the local percentage of gold is increased consequently. Therefore, both processes are gilding processes, the second being known as “depletion gilding”. It happens because a specific depletion process had been applied to the surface of the object or because it had been buried for a rather long time [1] (of course, besides such a slow gilding process, time is causing a long series of damaging and corrosive effects [2]). Masters of the depletion gilding were the pre-Columbian populations of America that used it for their “tumbaga”, an alloy of gold and copper, to give the luster of gold to the objects made of it. In this paper, we will discuss some aspects of tumbaga and depletion gilding. (See http://arxiv.org/ftp/arxiv/papers/1601/1601.00845.pdf for the rest of that paper.)
After an object was formed, the surface was treated to removed the alloys from the surface of the object. As a result the object looked gold, but the inside of the object might contain high amounts of alloys. Not only did that affect the appearance of the object, but it changed other properties of the object. High amounts of copper can make an artifact much more brittle than a higher purity of gold. That means you have to treat it more carefully.
Be careful how you store such items. They might not be as durable as you think. Don't just dump nice items into a box with a bunch of coins or something else.
Put them in individual containers so they won't touch other items, especially those made of other metals. And protect them from weight and pressure. I've learned those lessons the hard way.
You can learn more about tumbaga and Precolumbian metal working by accessing a preview of the book Rivers of Gold - Precolumbian Gold From Sitio Conte online. Click on the title to go to the preview.
While the conquistadors melted down most of the tumbaga, figures have been found, but it is almost impossibly rare.
The Tumbaga Wreck from the Bahamas (early 16th century) contained many tumbaga bars made from artifacts that had been melted. I think some tumbaga or tumbaga-like pieces made much later employed similar metallurgical techniques continued to be used by native populations.
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When you think of treasure you might think of pictures of pirate chests over-flowing with sparkling gold. You've seen the pictures in the movies and fiction books. On the other hand, if you think of things that are centuries old, you might expect them to look old. In both cases, you might be wrong.
Years ago I didn't know that gold was enameled back in the 18th century. When I saw a nice gold enameled ring, I quickly and wrongly concluded it was modern. I was wrong.
One thing you might easily misidentify is tumbaga. It can look like gold even though it can be anywhere from three percent to ninety-seven percent made of alloys such as copper and silver.
The Precolumbian natives encountered by the conquistadors knew how to work metals. They used alloys and gilding.
Many items that looked like gold even were actually of a much lower purity.
A phenomenon often encountered when ancient objects made of noble metal alloys are analyzed is that of their surface enrichment. Let us consider, for instance, a statuette made of an alloy of gold with copper and/or silver; it can occur that its surface has a percentage of gold higher than that of the bulk. This enrichment can be due to an addition of gold on the surface, or to a depletion process during which the less chemically stable elements leach out causing the surface composition to change. In both cases, the local percentage of gold is increased consequently. Therefore, both processes are gilding processes, the second being known as “depletion gilding”. It happens because a specific depletion process had been applied to the surface of the object or because it had been buried for a rather long time [1] (of course, besides such a slow gilding process, time is causing a long series of damaging and corrosive effects [2]). Masters of the depletion gilding were the pre-Columbian populations of America that used it for their “tumbaga”, an alloy of gold and copper, to give the luster of gold to the objects made of it. In this paper, we will discuss some aspects of tumbaga and depletion gilding. (See http://arxiv.org/ftp/arxiv/papers/1601/1601.00845.pdf for the rest of that paper.)
After an object was formed, the surface was treated to removed the alloys from the surface of the object. As a result the object looked gold, but the inside of the object might contain high amounts of alloys. Not only did that affect the appearance of the object, but it changed other properties of the object. High amounts of copper can make an artifact much more brittle than a higher purity of gold. That means you have to treat it more carefully.
Be careful how you store such items. They might not be as durable as you think. Don't just dump nice items into a box with a bunch of coins or something else.
Put them in individual containers so they won't touch other items, especially those made of other metals. And protect them from weight and pressure. I've learned those lessons the hard way.
You can learn more about tumbaga and Precolumbian metal working by accessing a preview of the book Rivers of Gold - Precolumbian Gold From Sitio Conte online. Click on the title to go to the preview.
While the conquistadors melted down most of the tumbaga, figures have been found, but it is almost impossibly rare.
The Tumbaga Wreck from the Bahamas (early 16th century) contained many tumbaga bars made from artifacts that had been melted. I think some tumbaga or tumbaga-like pieces made much later employed similar metallurgical techniques continued to be used by native populations.
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More Thoughts on the Archaeology Citizen's Archaeology Issue.
OK. You're not going to hunt arrowheads on state lands, so how would the proposed citizen's archaeology permit that I talked about yesterday make any difference to you?
If you looked at the links and the associated web sites, you might have run across the archaeologist's arguments against the permit. You might have noticed that the arguments are the same old arguments they use for everything. It boils down to "everything is extremely important and anything 50 years old or more must remain exactly where it is unless it is studied or collected by an archaeologist." Those are the same basic arguments you hear whether they are talking about a stone artifact, pot shard, coin or anything that is fifty years old. And the definition of "submerged lands," which once seemed to me to mean "navigable waterways" now includes streams, ponds, ditches, and I don't doubt will someday include puddles.
If the old arguments that everything over fifty years old must not be touched by anyone but an archaeologist is allowed to stand as it relates to the citizen's permit, the same unreasonable arguments will stand for every other situation.
A more reasonable approach would be better for both the public and archaeology. I presented some of my positions yesterday. I won't go through all of the arguments now. I'll just say that the current situation is largely counterproductive for both sides and that there are good solutions.
What the supposed failure of the Isolated Finds Program might tell us is that the public does not find artifacts as often as archaeologists might fantasize, or that people were not sufficiently informed or comfortable with the process. Their conclusion seems to be that the public is dishonest, selfish, stupid or simply criminal.
I just wanted to let you know that the issue has relevance to you even if you, like me, would never think of going out to hunt stone artifacts on state lands.
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The day will start with a north wind that will shift east. The surf will increase today up to around 3 - 5 feet where it will remain for it looks like a couple weeks.
Happy hunting,
TreasureGuide@comcast.net