The composition of most metal items can be identified, to some degree, through observations and by examining an objects' appearance. If you're unsure what type of metal an item is composed of, examination of the item's characteristics will provide you with helpful information. Examine the color, hardness, and weight of the metal. Most metal objects are composed of more than just one type of metal. Each type of metal contributes to the unique character of the item. Burial alters the composition of an item. Practically all metal items corrode, to some degree, when they are buried in the ground. Corrosion may be in the form of thin layers or thick disfiguring crusts that can greatly conceal the details of an object and make it difficult to identify. The level of corrosion that occurs is really dependent on the type of metal, the chemistry of the soil, and the period of time that an item has been in the ground. Different types of metals corrode differently. This blog discusses some of the different types of metals we find when out detecting and the corrosion that occurs to the item while it is in the ground. Corrosion can be your first visual clue to help you determine what type of metal an item is made of.
It can be rather easy to identify if an item is composed of iron. With iron items the challenge comes, sometimes, when you are trying to determine what the item actually is. Corrosion on iron is usually in the form of rust. Rust can be quite disfiguring and may make the identification of an item difficult to determine. An iron item that has spent some time in the ground will come out covered in rust and looking crusty. Corroded iron items are usually brown, reddish brown, or orange in color. An iron item that was burned in a fire may appear to be deep red in color. Generally speaking, most iron items are magnetic. A quick magnet test could also help you to determine if an item is composed of iron.
Copper items tarnish gradually over time changing to a dark brown or black color before finally turning into a distinctive blue-green color. A lot of the copper items you find in the ground will have a beautiful blue green patina to them. Some of the copper items you dig may be lightly corroded with a dark patina.
Brass is an alloy of copper and zinc. As brass corrodes in the ground, it usually undergoes dezincification, a process where it's zinc component is lost. Zinc dissolves when buried in the ground. As the zinc component disappears, it changes the composition of the item. The surface of corroded brass items are usually rich in copper. The brass items that we dig might be blueish green in color. Any item that contains a high amount of copper can turn green in color when buried.
Lead is non magnetic, relatively heavy, and soft enough that you could carve into it with a pocket knife. Objects made of lead are deceiving in that they are heavier than they actually look. The lead items that we dig have a white layer of crust on the surface of the object. This is due to white lead carbonate. It is also possible to find red lead oxide on the lead objects you dig, but that doesn't happen all that often.
Pewter items don't always hold up the best in the ground. Sometimes they will crumble right there in your hand after you pull them from the hole. Corroded pewter items can be cracked, crusty, or pitted with disfiguring warts. Old pewter items usually contain lead and may form a dark gray patina over time. The pewter items we find metal detecting may be marked with maker's marks. Maker's marks can help you to identify more information about the item such as where or when the item was made. Pewter is a soft metal though so the marks often get very worn with time. And unlike with gold and silver items, there was very little control over the marks used on pewter items. So, essentially, it may be a little more challenging to gather information from the marks that are on a pewter item.
Silver items might appear silvery in color when excavated. Sometimes when silver is exposed to light, after being in the ground, the surface turns a purplish grey color. Badly corroded silver items will be covered in a black patina. The black patina may make it difficult to determine if the item is made of silver. The silver items you find may have makers marks, hallmarks, and or purity markings. Makers marks just give you information about the designer or manufacturing company. Hallmarks are an official mark that attest to the item's metal purity. Hallmarks may also provide you with information about the office the metal was tested in, the year it was tested, and information about the designer. With purity markings, the first thing you want to pay attention to is the shape of the stamp. An oval stamp indicates that an item is composed of silver. The number inside the shape indicates the actual precious metal content or the purity of the metal. Silver items might also be stamped with the words silver or sterling, or stamped with numbers like 925 or 999. Silver plate items are also often marked. Silver plated items that you find with your detector may have some loss or damage to their surface. They tarnish over time and could rust depending on the makeup of their metal composition.
Gold in it's pure form .999 does not corrode. It retains its shine forever. Pure gold is an extremely soft metal that dents very easily. Due to it's softness, you don't often find pieces of jewelry that contain only the pure gold element. Gold jewelry is alloyed with other base metals. These other metals alter its properties. If these other base metals react with or to oxygen, sulfur and moisture the gold item may tarnish. Tarnish is a type of corrosion that forms on metal items that do not contain any iron. Gold jewelry with a higher karat count is less likely to tarnish than a piece of gold jewelry with a lower karat count. The gold items we find detecting will have some surface wear to them as well. Gold items are often marked with hallmarks, makers marks and or purity marks. Purity markings that are a rectangle shape with the corners shaved off indicate that an item is gold. Just like with silver purity marks, the number inside the shape indicates the purity of the metal. Gold might also be stamped 10k, 14k, 18k, ect. Gold items that you find while out metal detecting are usually easily identified by the naked eye. There may be times you might not know for sure though. A simple acid test can be done to confirm that the item is composed of gold and it's purity amount.
Listed below are a few other common marks and their meanings that might be helpful to know.
CW: Carat Weight
CZ: Cubic Zirconia
GF: Gold Filled
GP: Gold Plated
KP: Karat Plump
PMC: Precious metal clay
PT or PLAT: Platinum
RGF: Rose gold finish
RGP: Rose gold plated
SC: Silver colored metal
SLF: Silver finish
SLP: Silver plated
SS: Sterling Silver
SS or St Steel: Stainless Steel
SOL: Solitaire Diamond
Have a great week! Happy Hunting!