Many modern weapons like missiles and bombs have a sensor on the nose for Infra Red (IR), Laser, or GPS guidance. Typically the sensor is mounted behind a coated lens to protect the sensor and allow it to have a wide field of view. Many times modelers paint them using gloss paint. The below tutorial will show you how to replicate the coated lens appearance.
To start with, the tools required are a drill bit the size of the sensor, Liquitex Acrylic Gel medium (or similar product), silver or chrome paint (I used Model Master Chrome) and Tamiya X-19 Smoke paint. The smoke paint is a transparent black paint.
Here is a photo of a Russian R-3S missile in 1/48 scale from a MIG-21 kit.
Take the drill bit and drill into the missile to create a concave hole.
Next take the silver/chrome paint and paint the inside of the area. This is done so when complete the light will reflect thru the transparent black and give it depth and look like an actual lens.
After the paint dries, using the acrylic gel form the shape of the nose. This may take a couple of layers to build up to the correct shape. The gel is a milky white but dries to a golden clear. Some sensors will have a golden coated lens so you can stop here. If the lens has the black tinted coating, proceed to the next step.
Once the acrylic gel dries, paint the outside with the Tamiya Smoke. The level of tint can be set by the number of coats you paint on. This is after 3 coats.
While it is difficult to show in a photo, the light will reflect and give the sensor lens a very realistic effect. This method can also be used when making FLIR camera lens’ as well as targeting turrets on targeting pods of airplanes, helicopters, and vehicles.
Here is a quick video close to light source.
Happy Modeling!
Kit missile on left, Drilled, chrome paint and acrylic filled, and final on right.
David's Scale Models 
I use a similar process for nav and landing lights using Tamiya Clear Red and Clear Green, Micro Kristal Klear and then top coating with Future.
LikeLike
That is my other tip https://davidsscalemodels.com/tips-and-tricks/recognition-lights/
LikeLike
Hey David, I am not certain, but my guess is this tutorial was made before the creation of metallic stickers supposedly created for Gundam eyes/helmet lenses. Since this page was created, have you tried and tested these stickers? It looks like your missile heads will remain the best option. But the flat, large targeting pods found on many helicopters appear very well suited for these metallic stickers. I would promise a test and report regarding these stickers, but it probably won’t happen any time soon.
Thanks in advance, cheers,
Anthony
LikeLike
The stickers they make for Gundam models is the same thing as Bare Metal Foil. They work great for mirrored surfaces like helicopter sensors and pilot helmets. But for missiles the sensor heads are more like tinted lenses. The method I suggest gives the sensor heads more visual depth so it looks more realistic.
LikeLike
Thats exactly what I said actually. The convex nature of missile heads makes thivk(ish)stickers impractical. Plus, as you just said, the missile lens is very different than the optics for targeting pods found on many helicopters and attack aircraft.
As for my unique situation, I have been trying to find the product you recommend, but so far, I have only found acrylic gel that need UV light to cure them. Is that the sams thing, or absolutely the wrong product?
LikeLike
As long as it cures clear, it should work.
LikeLike