Only if the greatest importance is laid on the general and individual quality of a painting we could reach a level, that will allow us to also discuss paintings without a signature.
An interesting example is the great set of Shouki and blue magpies.
This painting performs on a very high level of competence, especially in the figure composition with its great use of ink only. The unsealed set is, with the way the birds and plants are executed, pointing to the beginning of the 17th century. But while the bird paintings are not easily attributed to a certain hand the central painting of Shouki is coming with a very distinguished individual brushwork. The main unique feature is the shape of the outline strokes of the figure. They look often like a deep scoop and this is such a peculiar way to start a brush stroke that it would be found easily in another painting of this master with a comparable subject.
In the picture below this peculiar starting point of the brush can be seen in many strokes, smaler or bigger. More evidence for this individual mark in the brushwork is easily discovered by clicking through the slide show in the museum section.
The painting easily by style and subject choice a work of a Kanou painter and dated around 1600. All what is left to do is to check the best masters of this time and the individual brush will show up again. The number to check on is by the quality limited to a very few possible names.
In the collection of the Metropolitain Museum already we find the scoops again in a painting of Hotei:
Now a name attached, it is easy to check other paintings to confirm the attribution.
This is a rather sure case, but it works also with painters with a less peculiar way to start a brush stroke.
Often though the situation is much less obvious and only a meagre result like “ It might be ...” or “we cant say” is achievable. But in the end it is much better to admit this, than pretending to know more while having no clue.
Authentication can only be achieved seriously with arguments. It has to be understandable.
Unfortunately authority is much easier to sell than arguments.