Hydrolytic Resistance of Glass Bottles

Glass is widely used for perfume, cosmetics, food, beverages and pharmaceutical packaging because of its transparency, barrier properties, chemical stability and premium appearance.

However, glass is not completely inert.

When a glass surface is exposed to water, moisture, heat or certain chemical environments for a long period, small quantities of alkali ions can migrate from the glass surface. Under unfavorable storage or use conditions, this may gradually lead to glass weathering, alkali bloom, white haze, surface spots or loss of transparency.

For packaging buyers, this is not simply a laboratory issue. A bottle that looks perfectly clear when it leaves the factory may spend several weeks at sea and several months in a warehouse before it reaches the filling line. If the glass composition, surface condition, packaging or storage environment is unsuitable, visible surface changes may develop during this period.

This is why hydrolytic resistance is an important indicator of glass bottle chemical durability.

In this guide, we explain what hydrolytic resistance means, why alkali bloom occurs, how glass containers are tested, what affects their chemical durability, and what perfume and cosmetic packaging buyers should consider when evaluating glass bottles.

What Is Hydrolytic Resistance of a Glass Bottle?

Hydrolytic resistance describes the ability of a glass surface to resist chemical attack by water.

When water contacts soda-lime-silica glass, an ion-exchange process can occur at the surface. Alkali ions—particularly sodium ions—can migrate from the glass and be replaced by hydrogen-containing species from the water.

The better the hydrolytic resistance, the lower the amount of alkali released under specified test conditions.

This property is particularly important when the contents remain in direct contact with the glass for long periods or when the container is exposed to elevated temperatures during processing. It is also a useful indicator of the overall chemical durability of a glass container.

Why Do Glass Bottles Develop White Haze or Alkali Bloom?

One of the most common visible forms of glass surface deterioration is described as:

· white haze;

· cloudy glass;

· white spots;

· alkali bloom;

· soda bloom;

· glass weathering;

· surface fogging;

· or glass blooming.

In some markets, the phenomenon is also informally referred to as “glass mildew.” The process generally begins with moisture.

1. Moisture Reaches the Glass Surface

Water molecules from humid air are adsorbed onto the surface of the glass. Even when a glass bottle is empty, moisture in the surrounding atmosphere can interact with the glass surface.

2. Alkali Ions Migrate

In conventional soda-lime-silica glass, mobile alkali ions, particularly sodium ions, can migrate toward the surface and participate in ion-exchange reactions with water. The surface therefore gradually becomes chemically different from the original bulk glass.

3. Alkaline Surface Products Form

The released alkali can react with moisture and carbon dioxide in the air. Over time, sodium-containing carbonates and other soluble alkaline compounds can accumulate on the surface. Because these compounds are often hygroscopic, they can attract additional moisture and accelerate further surface reactions.

4. Haze, Spots or Deposits Become Visible

As the process continues, the bottle may develop:

· a thin cloudy film;

· white crystalline deposits;

· rainbow-like stains;

· localized white spots;

· a slightly slippery surface;

· or, in severe cases, permanent loss of transparency.

At an early stage, some surface deposits may still be removable by cleaning. However, if the glass surface itself has already been chemically attacked, the resulting haze may become permanent.

Is Alkali Bloom the Same as Poor Hydrolytic Resistance?

Not exactly. This distinction is important.

Hydrolytic resistance is a laboratory measurement of how a glass surface behaves when exposed to water under controlled conditions.

Glass weathering or alkali bloom is a visible surface deterioration that can develop during storage or environmental exposure.

The two are related because both involve interaction between water and the glass surface, but they are not identical quality indicators.

A glass bottle may meet a specified hydrolytic resistance requirement and still require proper packaging and storage to minimize long-term weathering. For buyers, the correct approach is therefore not to rely on one test result alone. Glass composition, manufacturing conditions, surface treatment, packaging method, storage environment and intended contents should be evaluated together.

How Is Glass Container Hydrolytic Resistance Tested?

One internationally recognized method is ISO 4802-1:2023 — Glassware — Hydrolytic resistance of the interior surfaces of glass containers — Part 1: Determination by titration method and classification.

The principle of the test is relatively straightforward. A specified amount of water is placed inside the glass container. The bottle is then exposed to elevated temperature under controlled conditions. Alkali released from the inner glass surface enters the water.

The extraction solution is subsequently titrated with a standardized acid solution. The amount of acid required indicates how much alkaline material has been released from the glass.

A typical test procedure includes:

1.  Selecting the required number of glass containers.

2.  Cleaning the samples according to the standard.

3.  Filling them with the specified test water.

4.  Heating the containers under controlled temperature and time conditions.

5.  Collecting the extraction solution.

6.  Titrating the solution using a standardized acid.

7.  Calculating and classifying the result according to the applicable standard.

For formal quality control, the exact test temperature, filling volume, sample quantity, titration method and acceptance limits must always follow the applicable standard.

Understanding HCT1, HCT2 and HCT3 Glass Classes

Under ISO 4802-1 terminology, glass containers may be classified according to their inner-surface hydrolytic resistance. A simplified interpretation is:

HCT1

Glass containers with very high hydrolytic resistance. This category is typically associated with glass compositions such as borosilicate or neutral glass, where high chemical resistance is primarily achieved through the glass composition itself.

HCT2

Usually soda-lime-silica glass containers whose inner surfaces have been specially treated to improve hydrolytic resistance.

HCT3

Typically untreated soda-lime-silica glass containers with moderate hydrolytic resistance.

However, buyers should not simply specify the highest possible class without considering the actual application. Pharmaceutical, food, beverage, perfume and cosmetic packaging have very different performance and regulatory requirements.

A Note on GB/T 4548 in China

For glass containers manufactured and tested in China, GB/T 4548 is an important standard relating to the hydrolytic resistance of the inner surface of glass containers.

The new edition, GB/T 4548-2026, was published on April 30, 2026 and is scheduled to take effect on November 1, 2026.

Until its effective date, manufacturers and laboratories should confirm which edition is currently applicable to the specific inspection or customer requirement.

Various Chinese standards for food and beverage glass containers have historically specified hydrolytic-resistance requirements such as HC3. However, this does not mean that HC3 is automatically a mandatory requirement for every perfume or cosmetic glass bottle.

For fragrance and cosmetic packaging, the appropriate requirement should be determined according to:

· the destination market;

· the customer’s technical specification;

· the product formulation;

· applicable regulations;

· the agreed inspection standard;

· and the expected storage and use conditions.

What Factors Affect the Hydrolytic Resistance of Glass?

1. Glass Composition

Chemical composition is one of the most important factors. Soda-lime-silica packaging glass is primarily based on a silica network, with sodium, calcium and other oxides added to achieve suitable melting, forming and mechanical properties.

In general, a stronger and more chemically stable glass network reduces the mobility and release of alkali ions. Increasing chemical durability typically involves controlling the proportion and interaction of the oxides that form and modify the glass network.

Borosilicate glass normally provides higher intrinsic hydrolytic resistance than conventional soda-lime glass. This is one reason borosilicate glass is widely used in demanding pharmaceutical applications.

However, borosilicate glass is not automatically required for conventional perfume bottles, cosmetic bottles, beverage bottles or food jars. The correct glass type should always be selected according to the intended application.

2. Manufacturing and Annealing Conditions

Glass production does not end when the bottle leaves the mould. The melting process, forming temperature and annealing conditions can influence the final properties of the glass. Poor process control may create inconsistent performance even when the nominal glass composition remains unchanged. Correct annealing is particularly important for controlling residual stress and ensuring stable quality.

3. Inner-Surface Treatment

For some applications, the inner surface of soda-lime glass may be treated to reduce alkali release. This process is commonly referred to as dealkalization or internal surface treatment.

The purpose is to reduce the concentration or mobility of alkaline species at the inner surface of the bottle. Appropriate treatment can significantly improve the hydrolytic resistance of soda-lime-silica glass containers.

However, the treatment should be verified by standardized testing rather than assumed from the treatment process alone.

4. Temperature

Temperature strongly influences chemical reaction rates. A glass bottle stored for months in a hot warehouse can therefore experience more aggressive surface weathering than an identical bottle stored under cool and stable conditions.

This becomes especially important during international shipping. Shipping containers exposed to direct sunlight may experience significantly higher temperatures than normal indoor storage environments.

5. Humidity

Humidity is one of the main drivers of glass weathering. Water adsorbed from humid air provides the medium necessary for ion exchange and subsequent surface reactions. For this reason, long-term storage in tropical, coastal or otherwise humid regions requires greater attention.

6. Storage Time

Glass weathering is time-dependent. A bottle that looks perfect immediately after production may behave differently after six or twelve months of poor storage.

This is particularly relevant for imported packaging, where empty containers may move through the following chain:

The actual storage period can therefore be much longer than many buyers initially expect.

Why Hydrolytic Resistance Matters for Perfume and Cosmetic Glass Bottles

Perfume packaging is different from pharmaceutical packaging, but chemical durability still matters.

Appearance Is Part of the Product

A luxury perfume bottle is not merely a container. It is part of the brand experience.

White haze, surface fogging or visible alkaline deposits can make an otherwise functional bottle commercially unacceptable. A small visual defect that might be tolerated on a commodity container can be unacceptable on a premium perfume bottle displayed under strong retail lighting.

International Shipping Creates Harsh Conditions

Perfume bottles exported internationally may spend several weeks in containers and warehouses. Routes passing through the Middle East, Southeast Asia and other hot or humid regions can expose glass packaging to challenging environmental conditions. Glass quality therefore needs to be supported by suitable packaging and storage conditions.

Long-Term Inventory Increases Risk

Perfume brands often purchase packaging several months before filling. Packaging distributors may hold bottles for even longer periods. The longer the storage period, the more important it becomes to control humidity, temperature and inventory rotation.

Product Compatibility Must Be Evaluated Separately

Hydrolytic resistance is important, but it does not prove complete compatibility with a perfume formula.

Fragrance products may contain:

· ethanol;

· water;

· fragrance oils;

· colorants;

· solvents;

· fixatives;

· and other formulation ingredients.

For important projects, a compatibility test using the actual fragrance formula is more meaningful than relying only on the hydrolytic-resistance classification.

The complete packaging system should also be evaluated, including:

· glass bottle;

· pump;

· gasket;

· collar;

· dip tube;

· cap;

· and decorative coatings where relevant.

Does External Spraying or Frosting Improve Hydrolytic Resistance?

Normally, no.

Processes such as:

· color spraying;

· frosting;

· screen printing;

· hot stamping;

· decal decoration;

· metallization;

· and external coating

are mainly applied to the outside surface of the bottle. They should not be confused with internal surface treatment.

A sprayed or frosted perfume bottle may still have essentially the same inner-surface hydrolytic properties as the original clear bottle before decoration. This is an important distinction when reviewing a supplier's technical specifications.

How Can Glass Bottle Weathering and Alkali Bloom Be Reduced?

There is no single solution. The best results come from controlling several factors together.

Choose the Appropriate Glass Composition

The glass formulation should provide adequate chemical durability for the intended application. For conventional perfume and cosmetic packaging, properly manufactured soda-lime glass is widely used and suitable for most applications. For more demanding applications, higher-performance glass compositions may be considered.

Control the Manufacturing Process

Stable melting, forming and annealing conditions are essential for maintaining consistent quality from one production batch to another. Process control is just as important as the nominal glass formulation.

Use Inner-Surface Treatment When Required

When an application requires increased hydrolytic resistance, an appropriate internal surface treatment may be specified. The effectiveness of the treatment should then be verified by laboratory testing.

Keep Bottles Dry During Storage

Empty bottles should be stored in a dry and ventilated environment. Persistent condensation and high humidity should be avoided. Large temperature fluctuations that cause moisture to condense inside cartons can also increase the risk of glass weathering.

Keep Packaging Materials Dry

Cartons, partitions, trays and protective packaging should remain dry. Wet or moisture-absorbing packaging materials can create a localized high-humidity environment around the glass surface. This may accelerate the formation of haze or alkaline deposits.

Use Suitable Bottle Separation

Bottle-to-bottle contact can cause mechanical marks and may also trap moisture between adjacent glass surfaces. Proper cardboard partitions, trays or protective packaging can reduce both physical and moisture-related damage.

Control Inventory Age

A practical first-in, first-out (FIFO) inventory system is strongly recommended. The longer empty bottles remain in storage, especially in high-temperature and high-humidity conditions, the greater the risk of weathering.

What Should Buyers Ask a Glass Bottle Supplier?

When glass chemical durability matters, do not simply ask: “Is the glass quality good?” That question is too vague. Ask for measurable specifications.

A professional buyer may ask:

1.  What type of glass is used?

2.  Is the bottle made from soda-lime-silica or borosilicate glass?

3.  Which hydrolytic-resistance standard is used?

4.  What acceptance class is required?

5.  Has the inner surface received any special treatment?

6.  Is the test performed in-house or by an independent laboratory?

7.  What storage conditions are recommended?

8.  How long can the empty bottles normally be stored?

9.  Are production retention samples maintained?

10.  Has compatibility testing been carried out using the intended product formulation?

For perfume packaging, buyers should also confirm neck tolerances, pump compatibility, crimping performance and leakage resistance.

Is HC3 Good Enough for a Perfume Bottle?

There is no universal answer. This is an area where buyers sometimes make an incorrect assumption.

A hydrolytic-resistance class that is appropriate for one type of glass container should not automatically be applied to every other type.

For a conventional soda-lime perfume bottle, the appropriate specification depends on:

· fragrance formulation;

· expected storage period;

· destination climate;

· brand requirements;

· customer specifications;

· and applicable regulations.

If a customer specifically requires an HC or HCT classification, the requirement should be clearly written into the technical specification before mass production. For particularly sensitive formulations or demanding storage conditions, additional compatibility testing should be performed.

Can White Haze on Glass Bottles Be Removed?

Sometimes—but not always.

If the haze is caused mainly by early-stage soluble surface deposits, appropriate cleaning may restore the original appearance. If the surface reaction has already caused permanent chemical damage to the glass structure, cleaning may not completely restore transparency.

This is why preventing glass weathering is much better than attempting to repair bottles after long-term storage.

Is Clearer Glass Always More Chemically Stable?

No. Optical clarity and chemical durability are different properties.

A very clear high-flint perfume bottle may have excellent visual quality, but appearance alone does not determine hydrolytic resistance. Chemical composition, manufacturing conditions and surface treatment must also be considered.

Hydrolytic Resistance Is Only One Part of Glass Bottle Quality

A reliable glass container must satisfy much more than appearance. Depending on the intended application, quality control may include:

· hydrolytic resistance;

· residual stress;

· thermal shock resistance;

· impact resistance;

· internal pressure resistance;

· vertical load strength;

· dimensional tolerances;

· nominal capacity;

· wall thickness;

· base thickness;

· neck-finish dimensions;

· sealing performance;

· heavy-metal migration;

· decoration adhesion;

· leakage testing;

· and product compatibility.

For perfume packaging in particular, FEA neck tolerances, pump compatibility, crimping quality and long-term fragrance compatibility may be just as important as glass hydrolytic resistance.

A strong quality-control system therefore evaluates the bottle as part of a complete packaging system rather than judging it by one parameter alone.

Final Thoughts

Glass is chemically stable, but it is not chemically indestructible.

Water, humidity, heat and time can interact with a glass surface and cause alkali release, weathering and visible haze, especially when soda-lime glass is stored for long periods under unfavorable conditions.

Understanding glass bottle hydrolytic resistance helps manufacturers and packaging buyers identify these risks before they become quality problems or customer complaints.

For perfume and cosmetic packaging, the most effective strategy is to combine:

The goal should not simply be to purchase a glass bottle that looks perfect when it leaves the factory.

The real goal is to make sure that the bottle still looks and performs correctly after shipping, storage, filling and the entire life cycle of the finished product.

For custom perfume bottles, cosmetic glass packaging or projects requiring specific hydrolytic-resistance standards, Xuzhou Daxin Glass Products Co., Ltd. can incorporate agreed testing methods and acceptance criteria into the product specification before mass production.