In some places my Linea picnic table doesn't turn a nice grey, but really dark grey or black. Is the wood rotting?

We understand this can look alarming at first, but rest assured: in 99% of cases this is not wood rot. There are two main causes for this black colour:

1. Natural weathering: due to a combination of a lot of moisture (rain) and little sunlight, the silver-grey colour can turn into a dark grey or black tone.
2. Surface mould (the weather): Douglas fir wood is a natural product that 'lives'. When the wood stays wet for a long time, microscopically small mould spores from the air can settle on the surface. This does not affect the construction or the strength of the wood, but only gives a black visual discolouration on the outside.