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5 Ways to Improve Back-Painted Glass Opacity

5 Ways to Improve Back-Painted Glass Opacity

Published by Leonardo Calcagno


Back-painted glass is widely used in architectural and decorative applications, requiring effective glass paint to block light transmission and achieve an opaque finish. Inadequate opacity can lead to light passing through the painted glass, exposing underlying materials, adhesives, and supporting structures meant to remain concealed. Here, we explore five effective ways to enhance back-painted glass opacity.

Understanding Opacity

Opacity in glass paint refers to the paint’s ability to conceal or hide the surfaces beneath it. Achieving the desired opacity involves applying a light-blocking layer to the glass, typically on surface 1 or 2. According to the Supreme Paint Co., several factors influence opacity:

  • Refractive Indices Difference: The contrast between the refractive indices of the pigment and the medium.
  • Particle Size and Dispersion: The shape, size, and degree of aggregation of pigment particles.
  • Pigment Volume Concentration (PVC): The proportion of pigment in the vehicle.
  • Film Thickness: The thickness of the applied paint film.

The main factors affecting glass paint opacity are:

  1. Glass paint color
  2. Paint thickness
  3. Paint quality

1. Selecting the Right Color

Color selection plays a crucial role in achieving opacity. White and black are the most straightforward colors to achieve opacity with, using water-based glass paint technology. This is because white bases typically contain titanium dioxide, a pigment with a very high opacity rating. Conversely, colors like yellow, pink, red, and orange have lower opacity and require different application techniques to achieve satisfactory results.

To improve opacity with these lower-opacity colors:

  • Use a high-quality white base: This can enhance the opacity of lighter colors.
  • Dark colors: Black, grey, and brown typically achieve opacity with a thinner coating, making them more efficient for achieving the desired result with less paint.

2. Applying the Correct Paint Thickness

The thickness of the paint application directly impacts opacity. High-opacity colours such as grey and black often need only a thin coating (approximately four miles) to achieve opacity. In contrast, lower-opacity colours require thicker applications (6 to 9 mils) to reach acceptable opacity levels. However, increasing paint thickness can raise costs in both materials and labour.

Key points to consider for paint thickness:

  • Higher opacity paints: Require a single, thinner coat.
  • Lower opacity paints require one or two thicker coats, increasing application time and material costs.

3. Using High-Quality Paint

The quality of the paint significantly affects opacity. High-quality glass paints contain more expensive components, including a higher titanium dioxide ratio, improving opacity. Although these superior paints come at a higher cost, they often reduce the number of coats needed, ultimately saving labour and materials.

Factors influencing paint quality:

  • Ingredient quality: High-quality formulas use better ingredients and fewer fillers.
  • Titanium dioxide concentration: More titanium dioxide means better opacity and fewer coats needed.

Investing in high-quality paint can lead to better results and long-term savings.

4. Implementing a Backup Coating

A backup coating involves applying an additional paint layer, typically a dark grey, to improve opacity, especially for colours with inherently low opacity. For example, instead of applying multiple coats of yellow, one could use 1-2 coats of yellow followed by a coat of grey. This technique enhances opacity while protecting the primary paint layer from scratches and abrasions during transit and installation.

Steps for effective backup coating:

  • Apply primary colour adequately: Ensure sufficient coverage to prevent the backup grey from showing through.
  • Test coverage: Place the glass flat on a table, paint side down, and check for pinholes or light spots. If the colour appears true and even, it is ready for the backup grey coating.

Backup coatings not only improve opacity but also enhance the durability of the paint job.

5. Considering Installation Location

The installation location can significantly impact the perceived opacity of back-painted glass. In brightly lit areas, any weaknesses in opacity become more apparent, especially when using dark adhesives like black silicone. If the paint opacity is not 100%, these conditions can cause dark spots.

To address this:

  • Brightly lit environments: Require more sensitive attention to glass paint opacity.
  • Adhesive colour: Dark adhesives might necessitate thicker paint coatings or a grey backup to prevent dark spots from showing through.

Adjusting paint thickness or adding a backup coating can mitigate these issues, ensuring the desired aesthetic outcome.

Tools for Ensuring Proper Paint Thickness

Consistency in paint thickness is crucial for achieving opacity. Several tools can help measure and maintain the correct paint application:

  • Wet Film Thickness Gauge: This gauge measures the thickness of freshly applied paint. Simple yet effective, it uses teeth on its edges to indicate the thickness based on which teeth touch the paint.
  • Dry Film Thickness Gauge: This tool measures the thickness of the cured paint. While more advanced, it provides accurate results post-production. Note that the paint will thin out during curing, so dry thickness will be less than wet thickness.

Understanding and utilizing these tools can ensure the proper application thickness, balancing opacity and material efficiency.

High-Opacity Glass Paint Solutions

Selecting the right glass paint vendor is crucial for achieving the desired opacity. Different manufacturers offer varying formula strengths and weaknesses. Key metrics to consider when choosing a glass paint include:

  • Formula quality: Look for high-opacity formulas with minimal fillers.
  • Colourant concentration: Some formulas allow for a higher percentage of colourant without compromising adhesion.
  • Vendor expertise: Choose vendors with experience achieving the required opacity for large runs, ensuring an efficient application with fewer coats.

Glass Paint Technology (GPT) offers advanced formulations designed for high opacity, even with lighter colours, providing superior results with fewer coats. GPT works closely with clients to meet opacity requirements efficiently, whether using roll coaters, curtain coaters, or automated and hand spray applications.

For expert advice and high-quality glass paint solutions, contact Glass Paint Technology today to discuss your opacity concerns and learn how we can help you achieve the best results for your back-painted glass projects.