Cai

There is a practical dimension too that rarely gets mentioned in the etiquette arguments.

Wildlife. Continuous artificial noise displaces animals from the area around the trail. That affects other people's chance of seeing anything, and in sensitive seasons — nesting, calving — it has more than aesthetic consequences.

Safety. In some terrain you genuinely want to hear things: rockfall, a river you are approaching, weather coming in, another party calling, or in bear country, everything. A speaker in your ears or on your pack removes that channel.

Worth being honest that the second point cuts both ways, because in some regions deliberate noise is recommended precisely to avoid surprising large animals. But that argues for a bell or your own voice, not a continuous soundtrack that also masks what you are trying to hear.

One more thing to check before starting: whether the cloudiness is on the surface at all.

Some older plastic eyes have a painted backing behind a clear dome, and when that backing degrades the eye looks dull no matter how well you polish the front. A quick test is to wet the surface — if it goes glossy and dark while wet, the problem is the front and polishing will work. If it still looks cloudy, the damage is underneath and no amount of surface work will reach it.

One caution on spray adhesive with black card: test the peel on a scrap first.

Some black craft card has a coated surface that lifts when tape or adhesive is removed, leaving a pale scar that is far more visible than any pencil line. Repositionable adhesives are much safer here than anything described as permanent, even for a temporary application.

One thing to be aware of with titanium dioxide specifically: it is an extremely effective opacifier, so it is easy to overshoot into something that looks chalky rather than solid.

If you want a white that reads as a material rather than as paint, a very small amount of a second pigment often helps — a trace of blue or grey stops it looking yellowish, which pure white epoxy tends towards as it ages.

Also worth knowing that epoxy yellows over time with light exposure unless it is a formulation with ultraviolet stabilisers. A white piece shows that far more than a coloured one, so if the project will sit in daylight it is worth choosing a resin sold as non-yellowing.

On the yellow question specifically, because it is the sharpest form of the puzzle.

Spectral yellow — a single wavelength around 580 nanometres — stimulates your long and medium cones in a particular ratio. Red light plus green light together stimulate those same two cone types in a similar ratio.

Your brain receives the same pair of signals and reports "yellow" in both cases. The two are physically completely different — one is a single wavelength, the other is two — and they are perceptually identical. Pairs like that are called metamers, and they are the entire reason a screen with three colours of pixel can show you a photograph.

So mixing red and green light does not produce yellow light. It produces a mixture that your visual system cannot distinguish from yellow light, which is a different and much stranger claim.

The thing being glossed over is large: the RGB model is not a model of light. It is a model of the human eye.

There is nothing physically special about those wavelengths. What is special is that most human retinas contain three types of cone cell, each responding to a broad and overlapping range of wavelengths, with peak sensitivities in the long, medium and short parts of the visible spectrum.

Colour, as you experience it, is your brain's interpretation of the ratio of signals from those three types. Nothing more.

That single fact resolves your objections. Red, green and blue are primary because they are effective keys for driving those three channels relatively independently. Choose three lights that each stimulate mainly one cone type, and you can reproduce an enormous range of perceived colours by varying their intensities.

A species with four cone types would have four primaries and would find our screens comically impoverished. Several do.

Whatever joint you use, seal the whole model before painting.

Corrugated cardboard drinks water-based paint unevenly and the surface texture and joins show through. A coat of dilute PVA or a proper primer over everything makes the surface uniform, and after that a paper-taped joint and the panel beside it genuinely look the same.

Skipping this is the usual reason a well-made model still looks patchy.