Barium Sulphate paint (BaSO4) is a scientific-grade coating that exhibits near-perfect diffuse reflectance at levels up to 98% in the 250-2500nm (UV-VIS-NIR) wavelength range. SphereOptics supplies Barium Sulphate white reflectance paint as an affordable water-based formulation or as more convenient ethanol-based or ethanol pre-mix solutions. Barium Sulphate is used to coat integrating spheres, lamp housings, backlight reflectors and laser pumping chambers, in fact anywhere where you need efficient, uniform illumination.
Diffuse reflectance coatings and materials exhibit Lambertian reflectance, that property whereby the reflected intensity of light follows Lambert’s cosine law, or the reflected radiance (or luminance) is equal from all directions of view and illumination. Diffuse reflectance is the opposite of specular (mirror-like) reflectance.
Barium sulphate (BaSO4) coatings are scientific-grade paints that exhibit near-perfect diffuse reflectance at levels up to 98% in the 250-2500nm (UV-VIS-NIR) wavelength range. SphereOptics supplies barium sulphate white reflectance paint as an affordable water-based formulation or as more convenient ethanol-based or ethanol pre-mix solutions. Barium sulphate is used to coat integrating spheres, lamp housings, backlight reflectors and laser pumping chambers, in fact anywhere where you need efficient, uniform illumination.
Diffuse reflectance coatings and materials exhibit Lambertian reflectance, that property whereby the reflected intensity of light follows Lambert’s cosine law, or the reflected radiance (or luminance) is equal from all directions of view and illumination. Diffuse reflectance is the opposite of specular (mirror-like) reflectance.
Commonly referred to as “integrating sphere paint”, barium sulphate coatings can be used on almost any substrate material (glass, plastics, metal, wood) and are best applied by spray painting (airless spray gun). Spray painting allows you to layer the paint gradually; at 12-15 layers, you achieve the optimum thickness and maximum reflectance. Brush painting is possible to touch-up small chips on an already painted integrating sphere for example, but brush painting a bare surface will not yield good results. At the optimum coating thickness of about 0.5 to 0.6mm, 1 litre of barium sulphate paint will cover an area of approximately 0.25m2.
Our affordable water-based formulation provides good optical performance and avoids the added costs associated with alcohol-based paints (hazardous cargo restrictions and costs apply to those) but the water-based formulation does take longer to apply. Reckon on between 5-6 hours total including drying time between layers assuming a warm, dry environment and some forced air drying of the paint. The ethanol-based paints are more expensive to transport (there are also storage restrictions) but the solvent evaporates more quickly which reduces the overall coating time.
The water-based barium sulphate paint is available in standard volumes of 0.5 and 1.0 litres, and in value packs of 2 or 3 x 1.0 litre bottles.
The Labsphere ethanol-based formulation is available in 250, 500 and 1000ml volumes and as a 250ml bottle of pre-mix which requires an equal volume of spectroscopic-grade ethanol to dissolve it in. Because ethanol is flammable, special hazardous cargo restrictions apply to these paints, as do local storage requirements (excepting the pre-mix, this is not flammable). Because of this, the ethanol-based paints are much more expensive but the alcohol evaporates more quickly than water and the drying time between layers is much reduced. This helps to keep the overall time to coat a reflector to a minimum.
Coating Type | Barium sulphate (BaSO4) in water or ethanol solution |
Wavelength Range | 250-2500nm (useful range is 300-2100nm) |
Reflectance | Up to 98% (at optimum coating thickness of 0.5 to 0.6mm) |
Application Rate | 1 litre of coating will cover 0.25m2 at 0.5 to 0.6mm thickness |
Application Method | Spray painting. Brush painting is not recommended and will yield vastly inferior results |
Solvent* | Choose between water or ethanol-based solutions. Also available is a premix formulation that should be dissolved in an equal volume of spectroscopic-grade ethanol |
Thermal stability | Up to 80°C |
Substrate Compatibility | Metal, plastic, glass and wood |
* Please note that the Barium Sulphate ethanol solution is flammable and therefore treated as hazardous goods for transportation or storage.
Code | Description | Guide Price* |
Water-Based BaSO4 Coating | ||
SOC050 | 500ml Barium Sulphate coating (BaSO4). Packing unit in 500 ml bottle | POA |
SOC100 | 1 litre Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle | POA |
SOC200 | 2 litres Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle | POA |
SOC300 | 3 litres Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle | POA |
SOC500 | 5 litres Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle | POA |
SOC1000 | 10 litres Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle | POA |
SOSP1 | Spray pack, comprising: 1 x 500ml paint (SOC050); 2 x sprayers (SP); 1 x glass bottle (GL) | POA |
Ethanol-Based BaSO4 Coating | ||
WRC-6080-05 | 500ml Barium Sulphate coating (BaSO4). Packing unit in 500ml bottle. | POA |
WRC-6080-1 | 1 litre Barium Sulphate coating (BaSO4). Packing unit in 1 litre bottle. | POA |
BaSO4 Coating as Ethanol Premix | ||
WRC-6080-PM | 250ml Barium Sulphate coating (BaSO4) as a premix for ethanol solution. | POA |
* Price subject to change without notice. Please request current pricing from SphereOptics before placing order.
You will expect to have to apply between ten and fifteen layers of Barium Sulphate paint. This is achieved by spray painting to build up the paint thickness to between 0.5 to 0.6mm for maximum reflectance. You must allow each layer of paint to dry before application of the next layer.
The water-based formulation takes longer to dry between layers than the ethanol-based formulation. A typical application of 12-15 layers of the water-based paint will take 5-6 hours to apply, of which 95% of the time you are waiting for a coating layer to dry. This assumes that the atmospheric conditions are not too humid and some kind of forced air ventilation is used to accelerate the drying process. The ethanol-based paint dries much more quickly, thus reducing the overall painting time.
As a layer dries, it changes colour. When wet, the paint is darker and as it dries it becomes lighter. When the layer has dried, the next layer can be sprayed on. If you don’t see any colour difference between the underlying and new layers, you will have reached the optimum paint thickness and you can stop.
You can use the Barium Sulphate coating on metal, glass or plastic substrates. The surface must be free by fats, oils, or other contaminants. Areas which are not to be coated should be masked to prevent overspray. The finished coating consists of several layers, each layer has to be as thin as possible. The thickness of the finished coating is about 0.5mm. An increase of the coating thickness above 0.5mm will not increase the reflectivity of the surface.
Applying fewer layers of Barium Sulphate paint on top of a lower reflectance, white coating will not achieve the same net reflectance. Using less Barium Sulphate paint can be a false economy and will reduce the performance of an integrating sphere system.
Store an opened bottle of paint with the lid screwed on. Once opened, the barium sulphate paint has a limited shelf life which depends upon environmental factors.
Cleaning of a surface that is coated with Barium Sulphate is only possible using gentle compressed air. The paint is hydroscopic and cannot be cleaned with water.
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