1. Yes silph, there is a rule: when the “e” is followed by a pair of consonants, you say “é” like in “dessin, pression” or “è” like in “belle, bretelle, parisienne, guerre”…

2. Well, because it’s french 😛 and there are lot of exceptions about etymology and word evolution through ages.

The rule is that “e” is pronounced “é” or “è” when in the middle of a syllable, and “e” (like in “de”) when at the end of a syllable. Syllables always split double letters, so we have “des-sin”, and the first “des” is pronounced just like the word “des”.

There is a rule for accenting.

When trying to accent an “e”, you’ll write “è” whenever the vowel in the following syllable is a single “e” that’s either deaf or is pronounced “e”, and you’ll write “é” otherwise (ignoring the circumflex case).

That’s for consistency reasons with this rule that the 1990 reform corrected “événement” into “évènement”, changed the accenting in the future tense (“céder + ai” now is written “cèderai” instead of “céderai”), and in those unused “dussé-je” now written “dussè-je”.

The two-identical consonants in “dessin” are preventing the accenting of the “e”, but the pronunciation is consistent with the accenting rule.

Accent sur E : É ou È ?

— E dernière lettre d’un mot : É

« Liberté, Égalité, Fraternité ».

— E à la fin d’un mot et suivi d’un s au singulier : È

décès, après.

— si la syllabe suivante contient un e muet : on prononce le E : È, sinon il si prononce É, et on supprime l’accent si le E est suivi de deux consonnes

È : La guerre est mère de douleurs.

É : Des dessins dépouillés.

— Ê et Ë sont des E accentués qui observent d’autres règles.