Hiya all. I had a question about colored incandescents .


This below image by @LAllenLighting depicts a GLS lamp coated with an opaque glaze/paint from the inside.
Aside from GLS lamps, this kind of color application can be found in various shades (yellow, orange, green etc.) in various types of lamps from pygmies to tiny globes and of course GLS lamps:

(click to enlarge)


Not so common, however, is the type of incandescent coated from the outside with a translucent lacquer.
This type too can be found all the way from pygmies to small globes and of course GLS lamps, but the filament is actually visible when powered up.
I came across this type of coating on a pygmy lamp but I haven't found the time to upload the photos. In it's place, here is an example by @LightsAreBright27, almost identical to my lamp in the coating used:

(click to enlarge)

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Here are my questions about the second (translucent) kind of coating:

How are these lamps made commercially? What is the kind of liquid they are dipped into, how is it made and is it easily available or even possible to synthesize from other easily available chemicals?
I assume the liquid has to be heated for this to work, so at what temperature would it be feasible?
What is the chemical compound used for the blue color? I have only picked blue cause it is my favorite incandescent color but I'd still be happy to learn about any color for that matter.
How realistic is it to coat either a GLS bulb or any smaller lamp (like a pygmy) at home with such a lacquer to get that blue hue?

Anyone?
@James?

I am not aware of what is actually used in lamp industry, but for thermally stable dyes in blue and green, different phtalocyanine dyes seem to fit well. These are very robust molecules, capable of surviving up to 500C. Maybe, also very finely disperse powders (to avoid milky appearance) of classic inorganic blue pigments like prussian blue or cobalt blue will work.

You of course need a thermally stable lacquer. 2-component silicone will likely work. Also may be something more specialized like high temperature polyurethane or polyimide, which are used in high temperature wire coatings.

Hmm, cobalt blue plus silicone seems like something that won't be too hard, it's worth a shot. Although I'd love to try the professional methods, it's just way too expensive and not possible without a factory

Most of the incandescent lamp lacquers are applied by spray-coating rather than dip-coating because it allows thinner and more uniform coatings, although dip-coating can also work.

Cheap lamps use lacquers based on cellulose materials which show excellent adhesion to glass, resistance to heat (except blue), but are neither scratchproof nor weatherproof.  They tend to breathe over time, expanding and contracting as they absorb moisture and then dry out again, which can result in cracking.  More expensive acrylic based lacquers are rather better in terms of durability and it's possible to make a good blue coating, but they are still not really weatherproof, and will fade over time or on hot lamps.  For the best outdoor rated lamps, in 1965 GE introduced a greatly improved design for its Sign lamps which use a double coating : first a cellulose or acrylic coloured lacquer depending on the colour, and then a top coating of clear Lexan polycarbonate.  That hard outer shell makes them scratchproof and completely weatherproof, but the colours still degrade under solar radiation and on hotter lamps.

The final improved development of the 1970s was to use a silicone-based carrier.  In more recent years that is nearly always used for blue and purple colour lacquers due to its greatly improved thermal stability, and for reflector lamps which run hotter it's also quite common for the red lamps.  The better manufacturers may use silicone lacquers more widely for all colours, but this is not common because they are so much more expensive.

Many of these lacquers are supplied to lampmakers all around the world by the GE Lamp Chemicals Plant at the East 152nd Street Facility in Cleveland, Ohio.  They are still running today, but I am not sure they still make these lacquers.  You can find one of their older datasheets at https://www.lamptech.co.uk/Documents/Datasheets/Thorn%20-%20Datasheet%20-%20D%20MS%20-%20MB%20Photoprinting%20-%201985%20UK.pdf

The former Philips Lamp Chemicals Plant at Maarheeze also used to have a good range of the silicone-based lacquers, as featured in their old catalogue at https://www.lamptech.co.uk/Documents/Components/Philips%20-%20Lamp%20Components%20-%20Chemicals%20-%201982%20EU.pdf

Very informative reply, and it seems the one color I'm looking for is the hardest to achieve. I do not think weather proofing will be much of a necessity in my use case, but the fading is not something I"m looking forward to. I think I'll be going with a silicone adhesive with an off-the-shelf pigment as @RRK suggested, and I don't intend to use much more than 15W.
It's a nice datasheet and I just learned about daylight de-luxe lamps (6250K) but there isn't much about the pigment itself, which is pretty interesting. If blue turns out to be too hard to use/can't retain the color well, I'll try out the same with purple pigment as well. Thanks for the informative response!