What happens before decoration can affect the final result.
When glass is going to be painted, printed, coated, or otherwise decorated, the quality of the finished result depends on more than the glass itself.
The condition of the glass surface at the time of decoration, how long the glass has been stored, how it has been handled, environmental conditions, the coating system being used, and the decorator’s preparation process can all affect the final result.
For that reason, Glassnow encourages customers to discuss surface preparation with their painter, decorator, or other production partner before beginning production.
Why Glass Surface Preparation Matters
Glass may look perfectly clean while still having materials on its surface that can affect paint or ink adhesion.
During normal container manufacturing, protective surface treatments known as hot-end and cold-end coatings are commonly applied to reduce scratching and friction as glass moves through production, filling, transportation, and handling.
After production, additional factors can affect the surface, including:
- Handling and fingerprints
- Dust and airborne contaminants
- Moisture and condensation
- Temperature changes during transportation
- Humidity
- Packaging materials
- Warehouse conditions
- Length of storage
The National Glass Association also recognizes that storage, moisture, contamination, and handling can affect glass surfaces and recommends appropriate inspection, protection, and cleaning.
This means glass that decorates successfully immediately after manufacturing may require different preparation after several weeks or months of transportation and storage.
A Decoration Problem Is Not Automatically a Glass Defect
When paint, ink, or another coating does not adhere properly, it can be tempting to immediately attribute the problem to the glass.
However, poor adhesion by itself does not establish that the glass is defective.
Decoration performance can be affected by several variables, including:
- Surface condition at the time of decoration
- Cleaning and preparation
- Paint or ink chemistry
- Primers or adhesion promoters
- Application equipment
- Curing temperature and time
- Storage conditions
- Humidity and condensation
- Handling
- Time between manufacturing and decoration
Professional coating and adhesion suppliers routinely emphasize proper surface preparation. Glass surfaces should be clean and dry, and contaminants such as grease, oils, fingerprints, dust, and moisture can interfere with adhesion.
Supported by 3M’s technical guidance.
Does Every Piece of Glass Need to Be Cleaned the Same Way?
No.
There is no universal preparation method that is appropriate for every glass container and every decorating process.
Depending on the glass surface and decorating system, a professional decorator may use methods such as:
- Dry wiping
- Alcohol-based cleaning
- Specialized washing systems
- Degreasing
- Primers or adhesion promoters
- Flame or other surface treatment
- Additional drying or conditioning
These are examples, not Glassnow instructions.
The appropriate preparation process should be established by the painter, decorator, or other production partner based on the coating system and the current condition of the glass.
3M, for example, recommends different levels of preparation depending on the type of contamination and notes that heavier oils may require a degreaser before subsequent alcohol cleaning.
Why Fresh Glass and Stored Glass Can Behave Differently
Time matters.
Consider a newly manufactured container that is painted close to the glass factory. The surface has had limited exposure to handling, transportation, temperature changes, humidity, or prolonged storage.
That same container may behave differently after:
- Several weeks of ocean transportation
- Changes in temperature and humidity
- Warehousing
- Repacking or handling
- Additional storage before decoration
This does not necessarily mean something is wrong with the glass.
It means the surface condition at the time of decoration may no longer be identical to the condition immediately after manufacturing.
Industry guidance recognizes the importance of minimizing prolonged storage and controlling condensation and air circulation around stored glass.
Seasonal Conditions Can Matter
Environmental conditions may also affect the glass between production and decoration.
Glass transported or stored during hot, humid conditions may experience different surface conditions than glass handled in cooler, drier weather.
Condensation is particularly important when glass moves between environments with different temperatures.
This is another reason Glassnow recommends that the decorator evaluate the glass when it arrives rather than relying only on how similar glass performed during a previous production run.
What Should You Discuss with Your Painter, Decorator, or Other Production Partner?
Before beginning a production run, ask your production partner:
- Do you normally prepare or clean glass before decorating it?
- What preparation does your specific paint, ink, or coating system require?
- Does your process require the glass to be free of manufacturing surface treatments, oils, moisture, fingerprints, or other contaminants?
- What cleaning or surface treatment do you normally use?
- Does the age or storage history of the glass affect your process?
- Do temperature, humidity, or condensation affect your decoration system?
- Will you perform an adhesion test before beginning full production?
- What incoming inspection do you perform before accepting glass for decoration?
These conversations are especially important when working with a new decorator, a new paint system, a new glass design, or glass that has been stored for an extended period.
Test Before Full Production
One of the most important steps is also one of the simplest:
Test the actual glass with the actual decoration system before beginning a full production run.
Professional surface preparation guidance consistently recommends evaluating adhesion and preparing the substrate for the specific application rather than assuming all surfaces will behave identically.
A small production test allows the decorator to identify whether additional cleaning, preparation, primer, curing adjustments, or other changes may be necessary before a large quantity is decorated.
What Happens if a Decoration Problem Occurs?
If paint, ink, coating, or another decoration does not perform as expected, Glassnow recommends reviewing the complete process before determining the cause.
The review should include:
- Glass lot and production information
- Date the glass was received
- Length and conditions of storage
- Cleaning or preparation performed
- Paint, ink, coating, and primer used
- Application method
- Curing conditions
- Environmental conditions
- Adhesion testing performed before production
- Samples of both decorated and undecorated glass
Glassnow is happy to investigate legitimate glass quality concerns.
However, a decoration or adhesion failure alone does not establish that the underlying glass has a manufacturing defect.
Determining the cause requires evaluating both the glass and the decoration process.
Glassnow’s Role
Glassnow’s role is to supply quality glass containers and provide customers with information that can help them have an informed conversation with their painter, decorator, or other production partner.
We do not recommend one universal cleaning or preparation process because decorating systems vary considerably.
Your decorator is responsible for determining and validating the preparation, application, and curing process appropriate for their materials and equipment.
Our goal is simple:
Help everyone involved understand the glass, ask the right questions, test before production, and identify potential issues before they become expensive problems.