A piece of gold will usually be stamped with a mark indicating its type. A stamp of “GF” or “HGP” indicates that the piece is gold-plated, not pure gold. In contrast, a pure gold piece of jewelry may show a “24K” or other marking indicating fineness. Hallmarks are usually located inside the band of rings or near the clasp on necklaces.  However, be aware that some hallmarks can be faked. This is why it’s important to use a mark as only one of many indicators of authenticity. The hallmark may be very small. You might even need a magnifying glass in order to see it clearly. Turn on a bright light or lamp. Hold the piece close to the lamp’s light. Rotate it in your hand, so that you can examine all of the edges in particular. If you see that the gold appears faded or worn away at the edges, then it’s likely wear on the plating. This means that piece isn’t pure gold. If you hold the piece under a bright light, do you notice white or red spots anywhere on it? The spots may be very tiny and difficult to see. That is why it’s important to examine the piece under a bright light and maybe with a magnifying glass. These spots indicate that the gold plating may be wearing away showing the metal underneath. Hold a magnet directly above the piece. Lower the magnet until it is almost touches the surface of the item. If you feel as if the magnet is being drawn or pulled downward, then the item is not pure. The other metals in the item, such as nickel, are responding to the magnet. A pure gold piece will not draw the magnet, since non-ferrous.

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Write a summary of the previous text in Vietnamese:
Tìm ký hiệu trên bề mặt món đồ. Quan sát xem xung quanh cạnh của món đồ có bị bạc màu không. Tìm các đốm trên bề mặt món đồ. Đặt nam châm gần sát vào món đồ có thể là vàng.