Aluminum paste discoloration is one of the most common challenges faced by the coatings, inks, plastics, and metal coatings industries. Understanding the causes of discoloration and how to prevent it is crucial for product stability and long-term performance.

As one of China's leading manufacturers of metallic pigments, Zhangqiu Metal Pigment Co., Ltd. has nearly 40 years of technical experience and is committed to providing reliable solutions for aluminum pigments.

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What Is Aluminium Paste and Why Oxidation Matters

Aluminum paste consists of fine aluminum flakes dispersed in a solvent system. These flakes impart brightness, metallic luster, and hiding power to the coating.
However, aluminum is a reactive metal, meaning it readily reacts with oxygen, moisture, and acidic/alkaline substances. This reaction leads to oxidation, directly causing color changes.

Common Signs of Oxidation

• Dulling or darkening of metallic color

• Loss of brightness or sparkle

• Gas release or thickening in the paste

• Poor orientation, lower hiding power

• Yellowish or greyish tones after application

According to industry testing standards (ASTM D4214, ISO 9227), aluminum flakes show measurable color deviation after exposure to moisture and salt spray, confirming oxidation sensitivity in uncontrolled systems.

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Typical Reasons Aluminium Paste Changes Color

1. Moisture Exposure (Most Common Cause)

Water triggers oxidation rapidly. Even small moisture content in solvents, pigments, or fillers can cause aluminum flakes to react.

Typical situations:

• Improper storage conditions

• High humidity environments

• Incompatible water-based systems without proper treatment

Data Reference:
Studies show that free moisture above 0.15% can accelerate oxide layer formation on aluminum flakes within hours.

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2. pH Instability in Formulations

Aluminium reacts strongly under high-alkaline or acidic conditions.

Risk levels:

• pH < 6 promotes hydrogen release

• pH > 8 attacks the oxide layer on flakes

This results in color shifts, gas generation, and flocculation.

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3. Poor Compatibility With Resins or Additives

If aluminium paste is mixed with incompatible resin systems, the flakes can lose surface protection, leading to:

• Uneven dispersion

• Flocculation

• Oxidation spots

• Visible streaking or color inconsistency

This issue is particularly seen in low-grade or recycled resin systems.

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Application / Deeper Comparison

When comparing different application systems:

Oil-based coatings (most common)

• Better stability

• Lower moisture exposure

• Higher brightness retention

Water-based coatings

• Require special surface-treated aluminium paste

• Higher sensitivity to pH and moisture

Resin-coated aluminium paste

• Strong oxidation resistance

• Higher storage stability

• Better dispersion

• Ideal for demanding industrial coatings

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Your Trusted Aluminium Paste Expert

Color change in aluminium paste is predictable, preventable, and manageable with the right formulation strategy and raw materials.

If you need:

• Oxidation-resistant aluminium paste

• Resin-coated metallic pigments

• Technical troubleshooting

• Custom metallic effects

Contact the technical team at ZHANGQIU METALLIC PIGMENT CO., LTD.

info@zqmetallic.com
https://zqmetallic.com/

We help global coating, ink, and plastic manufacturers solve metallic pigment challenges with confidence.