Top 5 Ways to Help Improve Back Painted Glass Opacity

Back painted glass applications require the glass paint to block light transmission and create an opaque result so learn these ways to help improve back painted glass opacity.

Glass fabricators know that without opacity the glass remains semi translucent or transparent. This is considered a failure in Architectural or Decorative Glass applications. In other words, an opacity failure is when light transmits through the painted glass surface revealing the material, adhesives and supporting structure that is intended to be hidden or concealed.

Top 5 Ways to Help Improve Back Painted Glass Opacity

Top 5 Ways to Help Improve Back Painted Glass Opacity


What is Opacity?

Opacity, as it relates to Glass Paint, describes the “hiding strength” or “concealing power” of paint. Opacity on glass is achieved by applying a light blocking layer on surface 1 or 2.

The Supreme Paint co provides this clarification:

The hiding strength (or opacity) of paint is largely influenced by the difference of the refractive indices of the pigment and the medium, particle size and dispersion of the pigment (i.e. particle shape and degree of aggregation of the particles), the proportion of pigment in the vehicle (i.e., pigment volume concentration or PVC) and the thickness of the applied film. These factors determine the opacity of a particular paint.

We know that there are 3 main factors affecting Glass Paint Opacity:

  1. The glass paint color
  2. Thickness of paint applied
  3. The quality of paint used

How does Color affect Opacity?

The easiest colors for back painted glass to achieve opacity is white and black using our Glass Paint Technology water based product.

Our white bases contain white titanium dioxide which has a very high opacity rating.

Some colors have a lower opacity like yellow, pink, red and orange.

These low opacity colors require a different application approach.

How does Paint Thickness affect Opacity?

The naturally higher opacity paints like grey and black only require +/- 4 mil coating or one coat.

Most of the lower opacity colors require 6 to 9 mils (one to two coats) to reach acceptable opacity.

Thicker coatings increase costs in materials used and labor to apply.

Does the Quality of the Glass Paint affect Opacity?

High quality formulas require more expensive components.

A higher ratio of white titanium dioxide increases the cost of the glass paint but often reduces the thickness of the coating required to reach acceptable opacity.

Here are Top 5 Ways to Help Improve Back Painted Glass Opacity

What are the Opacity Implications of the Color we are using?

We know that lighter colors (like yellow, pink, red and orange) may require or more coats.

Using a high quality white base will help improve opacity.

Dark colors like Black, Grey and Brown provide opacity with a thinner coating.

What is a Backup Coating and how does it Improve Opacity?

A backup coating offers a glass paint layer that creates opacity.

Our backup color is a dark grey color used on the back of brighter (low opacity) colors.

For example, if you are applying a bright yellow color, instead of painting 3-4 coats to hopefully create opacity, you can do 1-2 coats of yellow and 1 coat of grey.

The grey backup paint not only creates great opacity with less paint, it will protect the yellow coating from scratches and abrasions during transit and installation.

The color on surface two remains true and accurate, while the grey on the back will only be seen on the coating side.

When using a backup grey always make sure you apply enough of the desired color down first, so the grey doesn’t leak through the coating side.

Test your coating coverage by placing the glass flat on a table, paint side down. Look for pin holes or light spots in the coating.  If the color looks true and even, you know it is ready for backup grey coating.

Please let us know if you have any questions about this, we can help you with the best grey color for this application.

Does the Back Painted Glass installation location affect Opacity?

If the Back Painted Glass is to be installed on a wall in a brightly lit area you will need to be more sensitive to the glass paint opacity.

Opacity weakness is often revealed when using black silicone adhesive to secure the back painted glass to a wall.

When the adhesive is darker than the paint color, opacity is not 100% and the environment is brightly lit there is a risk that adhesive will create dark spots.

As mentioned earlier, when you recognize these conditions you may choose to apply a thicker coating or add a back up grey.

What tools are available to ensure the desired Glass Paint Thickness?

There are several tools available to create consistency in your paint thickness.

Ensuring you apply a thick enough coating to create an opaque finish is one of the most important ways to help improve back painted glass opacity. It is also important to know how thick you are applying the paint as to not over or under apply.

Over applying is one method to ensure opacity, however you don’t want to waste paint either.

Here are a couple instruments that help you find out how thick you are applying your paint:

Wet Film Thickness Gauge

The Wet Film Thickness Gauge is very simple yet very effective.  Using the teeth on the outside of the instrument, you simply apply those to the freshly applied paint and depending on which teeth mark it touches, that is how thick you are applying the paint.

Below is an example of what a wet film thickness gauge looks like.

Wet Film Paint Thickness Guage that can be used to ensure a thick enough coating is applied to achieve opacity and Ways to Help Improve Back Painted Glass Opacity

Here is a YouTube video which easily explains how to use this tool: explains that;

This is how to measure using a wet film thickness gauge, also known as a wet film comb.

Wet film combs measure wet film thickness, and are available in a variety of materials including stainless steel, aluminium and plastic, with various measurement scales ranging from 20µm to 3000µm.

How to measure wet film thickness using a wet film comb: place a comb perpendicular to and touching the substrate. Hold the comb in position and wait a few seconds until the teeth are wet. Remove the comb from the film. The wet film thickness lies between the biggest value ‘coated’ or ‘wet’ tooth and the smallest value ‘uncoated’ or ‘dry’ tooth.

Dry Film Thickness Gauge

The Dry Film Thickness Gauge is used for the same purpose as a wet film thickness gauge, to understand how thick the cured coating is.

The only difference between the wet and dry film gauge is that a wet film thickness gauge can only be used during production. While the dry gauge can only be used in post production.

This tool is a little more advanced to deliver accurate results.

However, it is important to know that the thickness will be different wet vs dry.  During the curing process, the coating will lose thickness and be much thinner once dry.

Below is a picture of what the Elcometer dry film thickness gauge looks like:

THis is a photo of a dry film gauge to help Ways to Help Improve Back Painted Glass Opacity explains that;

Using the gauge is easy – there are no complicated instructions; just icons – which guide you through each function of the gauge.

Calibration is straightforward too; just select 1 point, which just uses an uncoated substrate. Or 2 point calibration, which uses an uncoated substrate and a calibration foil. Then follow the gauge prompts.

With its clear, large colour display, auto rotate and auto brightness. The Elcometer 415 is easy to read whatever the conditions.

The Elcometer 415 also comes with USB, or Bluetooth or both. So, as each measurement is taken, the reading can be instantly transferred to your PC, or Android or Apple mobile device, for professional report generation. Either by using our ElcoMaster data management software or your own inspection app.

Here is a YouTube video which easily explains how to use this tool:

Who Offers a High Opacity Glass Paint for Back Painting?

It is important to understand the formula strengths and weaknesses for Architectural and Decorative Glass Paint for back painting applications.

Here are some key metrics to look for as you make you make your Glass Paint vendor selection:

  • Formulas vary from manufacturer to manufacturer and so does the Opacity strength.
  • Some formulas can work with a higher percentage of colorant but the adhesion is weakened,
  • Some formulas include more high quality ingredients and less filler.

Glass Paint Technology has invested in a higher quality formula that creates a more opaque coating even with lighter colors AND we can accomplish the desired opacity with less paint!

In fact GPT works with companies to achieve the required opaqueness, especially on large runs where anything other than 1-2 coats is unacceptable.

And we have gained a lot of experience learning ways to help improve back painted glass opacity while working with roll coaters, curtain coaters and automated or hand spray applications. We have seen it all!

So please Contact Us today to discuss your opacity concerns and learn how we can help you.