Composition of brass:
Brass is a copper alloy primarily composed of copper (Cu) and zinc (Zn). It is the most common copper-based alloy, with a zinc content generally ranging from 3% to 45%. This alloy is formed by fusing copper and zinc in a specific ratio. This alloying process imparts many properties to brass that distinguish it from pure copper and zinc.
When the zinc content is low, brass more closely resembles pure copper, with a reddish color and a softer texture.
As the zinc content increases, the color of brass gradually changes to a golden yellow, becoming more and more like gold! Its hardness and strength also increase accordingly. For example, brass with a zinc content of 3%-10% has a lighter reddish color, while brass with a zinc content of 30%-40% has a distinct golden yellow color and is much stronger.
There are many grades of brass, which are categorized as common brass and specialty brass.
Common brass grades begin with an H, followed by a number indicating the copper content. For example, H62 brass has a copper content of 62% and a zinc content of 38%.
Common brass grades include: H62, H65, H68, H70, H80, H85, H90, and H96.
Each grade has different properties and uses.
The brass grades that most closely resemble gold are H80, H85, and H96.
H96 is the closest match! H96 brass contains approximately 96% copper and 4% zinc, resulting in a bright golden-yellow color similar to lower-purity gold, such as 18K gold. Under good lighting, after fine polishing, H96 brass can mimic the luster and color of gold. H96 brass is a common material used in imitation gold ornaments.
H85 brass is generally used for a vintage look. Its 15% zinc content makes the brass slightly lighter in color than H96 brass, while still retaining its golden color. For decorative items that require an antique or vintage look, H85 brass can effectively simulate the patina of aged gold, creating a rustic "golden" feel.
H80 brass is made by adding 5% zinc. This increased zinc content reduces the cost. H80 brass maintains the golden color and is commonly used in decorations, ornaments, and jewelry.
So how do you distinguish brass from gold?
Differentiation by sight requires experience and is difficult. Weighing brass also requires experience, as gold is generally heavier than copper.
If physical testing is used, consider hardness and density.
Hardness Test: Brass is harder than gold. Simple tools can be used, such as gently scratching an inconspicuous area with an ordinary steel needle.
Brass is not easily scratched, and even if scratched, the marks are shallow, with some burrs or roughness around the edges.
If brass and gold items are bumped against each other, brass generally won't deform noticeably, while gold, due to its softness, may deform. When identifying gold jewelry, gently scratch an inconspicuous area like the inner ring or back of the jewelry with a sharp object to initially determine whether its hardness meets the characteristics of gold.
Density Test:
Brass has a density of approximately 8.4-8.9 g/cm³.
Gold has a density of approximately 19.32 g/cm³, much higher than brass.
You can measure the volume of an object using the displacement method, then measure its mass with a balance, and then calculate its density using the density formula (density = mass ÷ volume). If the calculated density is within the density range of brass, it is likely brass. For a regularly shaped brass block, first measure its side length to calculate its volume, then weigh its mass to calculate its density.
Of course, chemical identification can be performed by observing the reaction of the two with acid.
For example, when brass is placed in dilute hydrochloric acid, bubbles will form. The reaction equation is: Zn + 2HCl = ZnCl₂ + H₂↑. This reaction is quite obvious and can be used as an important indicator for identifying brass.
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