the lord of the rings - What do Orcs and Trolls actually look like, or rather how did Tolkien imagine them?

Bear with me, while the question seems sort of ridiculous because the movie of Jackson and fantasy-role playing games presented them in detail, in fact the original Tolkien does not describe their features.

Orcs are ugly and are a bit smaller than humans, but apart from that there is very scarce information about their appearance or even if their members are looking alike or very different in stature and looks. We know that the Uruk-hai were stronger and bigger than the cave orcs and some specific orcs like Grishnakh are mentioned for their long arms, but essentially that was it.

The troll in Moria had a toeless foot and a skin which looks like a net over skin, but apart from very strong and very big there is not much information about trolls either.

So had Tolkien a specific image in mind or did he deliberately left it open to give the reader their own suggestion ? Are there drawings or descriptions outside LOTR from Tolkien ?

Answer

In Letter 144 Tolkiens says that Orcs

...owe a good deal to the goblin tradition, especially as it appears in George MacDonald.

These goblins are grotesque humanoids, slightly smaller than humans, hating sunlight, song and have weaknesses in their feet. Tolkien commented in letter 144 that he didn't like this last aspect of them.

Later in Letter 210 Tolkien describes Orcs as such:

...they are (or were) squat, broad, flat-nosed, sallow-skinned, with wide mouths and slant eyes; in fact degraded and repulsive versions of the (to Europeans) least lovely Mongol-types

In Letter 153 Tolkien admitted the following about Trolls

I am not sure about Trolls

And the way the trolls change from the dull witted cockney trolls from the Hobbit, to the impervious to sunlight brutes that are the Olag-Hai.

Which Tolkien addresses further on in Letter 153

I do not know about Trolls. I think they are mere 'counterfeits', and hence...they return to mere stone images when not in the dark. But there are other sorts of Trolls beside these rather ridiculous, if brutal, Stone-trolls, for which other origins are suggested

A sentiment shared by Treebeard

But Trolls are only counterfeits, made by the Enemy in the Great Darkness, in mockery of Ents, as Orcs were of Elves

_{The Two Towers - Treebeard}

As far as Troll looks, we are given glimpses through which we can begin make up a picture of them.

The cave trolls are described in the Lord of the Rings as such.

There was a blow to the door that made it quiver; and then it began to grind slowly open, driving back the wedges. A huge arm and shoulder, with a dark skin of greenish scales, was thrust through the widening gap. Then a great, flat, toeless foot was forced through below.

_{The Fellowship Of The Ring - The Bridge of Khazad-dûm}

Hill trolls out of Gorgoroth are described thusly

... Taller and broader than men they were, and they were clad only in close-fitting mesh of horny scales, or maybe that was their hideous hide and ...reaching out a clutching claw; for these fell creatures would bite the throats of those that they threw down

_{Return Of The King - The Black Gate Opens}

Which paints a picture of a scaly green creature of huge size and strength with claws and fangs capable of biting a throat out of a victim.

The vagueness and lack of description of the features would most likely be explained by Tolkiens self confessed "doubts" about trolls