Why can the same shade of color look different every time on glass?

7 Factors That Affect the Final Appearance of Glass Paint

When you order a specific shade of glass paint, you expect the final decoration to look the same every time it’s applied. That expectation is completely natural. However, it can happen that two products decorated with the same paint don’t look exactly the same.

The cause, however, may not lie in the paint itself. The final shade and overall appearance of the decoration are influenced by the entire production process—from paint preparation and application method to drying, firing, and the lighting under which we evaluate the finished product.

Let’s take a look at the most important factors that can influence the final color.

1. Paint Viscosity

One of the basic parameters is viscosity, or the thickness of the paint.

Before application, viscosity is typically adjusted by adding the recommended amount of water or thinner, depending on the type of paint used. However, if each worker prepares the paint based on their own judgment or prefers a different consistency, the amount of paint applied to the glass may vary.

This does not automatically mean that one application method is correct and the other is incorrect. If the resulting decoration is of high quality and free of defects, both procedures may be technically acceptable. Within a single production order, however, the viscosity should be precisely determined, regularly checked, and adhered to by all workers.

After the water or thinner evaporates, only a dry layer of paint remains on the surface. It is precisely the amount of this layer that can significantly affect the resulting intensity and appearance of the shade.

2. Workplace Temperature

Paint viscosity also varies depending on the ambient temperature.

During the warm summer months, the paint may naturally be thinner without the addition of water or thinner. In cooler conditions, on the other hand, it usually thickens.

Therefore, it is not advisable to assess the paint’s readiness based solely on the operator’s experience or intuition. Viscosity must be checked regularly, and current workplace conditions must be taken into account when adjusting it.

3. Coating Thickness

The amount of paint applied has a significant impact on the final color. The same shade can appear lighter, darker, or more intense depending on the thickness of the coat.

The resulting coating is primarily influenced by the application technology used:

• with manual spraying, it depends on the equipment settings and the operator’s experience;
• in screen printing, the screen, squeegee, print settings, and application method are decisive;
• for roller coating, the machine settings, the rollers used, and the ink viscosity all play a role.

Checking the amount of ink applied should therefore be a standard part of quality control, especially during the production of larger batches.

4. Drying and Firing of the Ink

The drying or firing process can also affect the final shade.

Differences in temperature, firing duration, kiln throughput speed, or other parameters can cause visible changes in certain shades. Attention must therefore be paid not only to paint preparation and application but also to all subsequent process steps.

To achieve consistent results, drying and firing conditions should remain as stable as possible throughout the entire production run.

5. Type and Production Batch of Glass

The final appearance of the decoration is also influenced by the glass itself.

Different types of glass may vary in their inherent color, transparency, or optical properties. These differences become particularly apparent when evaluating the decoration through the glass, such as when paint is applied to the back of a glass pane (so-called “position 2”).

In large-scale architectural projects, minor differences may arise even between production batches of the same type of glass. Therefore, whenever possible, we recommend producing larger projects using paint from the same batch and glass from the same batch.

6. Paint Production Batches

For larger projects, it is also safest to use a single paint production batch.

At GDS Technology, we manufacture paints according to precisely defined formulas, using electronically controlled dosing and established production tolerances. However, some pigments and other raw materials may exhibit slight natural variations.

Therefore, when dividing a large order among multiple production batches, we recommend performing a comparison check before beginning application. The ideal solution is to order the required amount of paint all at once, including an adequate reserve for any necessary touch-ups or additional production.

7. Lighting Conditions for Evaluating Color Shades

The final important factor is the lighting under which the finished decoration is evaluated.

The same product may look different:

• in daylight,
• under LED lighting,
• under fluorescent lights,
• under warm or cool artificial lighting.

This phenomenon is due to the fact that different light sources have different spectral compositions. As a result, two shades may appear nearly identical under one type of lighting, while a visible difference may appear between them under another.

Shade comparisons should therefore be conducted under predetermined and repeatable lighting conditions. In our laboratory, we use professional light boxes that allow us to evaluate colors under various standardized light sources without the disruptive influence of the surrounding environment.

How to Achieve a Consistent Shade Across an Entire Production Run

To achieve the most consistent result possible, we recommend:

• using glass from a single production batch,
• for large-scale projects, also use glass from the same batch,
• accurately determine and control the paint’s viscosity,
• maintain consistent application parameters,
• monitor the amount of paint applied,
• maintain the same drying or firing conditions,
• compare samples under standardized lighting,
• archive the approved reference sample.

Consistent recording of process parameters facilitates not only ongoing quality control but also the potential repetition of the order in the future.

The final color is the result of the entire process

When decorating glass, it is not only the paint formulation that matters. Equally important is how the paint was prepared, applied, dried, or fired; the type of glass on which it was applied; and the lighting conditions under which the final product is evaluated.

A consistent appearance across an entire production run can be achieved primarily through rigorous control of all production steps.

Paint can be produced according to a precisely defined formula. However, the same result is achieved only when the entire processing procedure is under control.

Do you need to establish a suitable production process, select a color for glass, or objectively compare the resulting shades?

At GDS Technology, we can assist you with expert consultation, laboratory measurements, and the preparation of samples for specific applications.

Article written by:
David Batla
Owner of GDS Technology s.r.o.