Lewis and Clark & Company brain tanned hides along the trail, much like home tanners do today. Brain tanned buckskin was vastly more durable than homespun and was commonly used throughout the frontier from the late 1600's through the late 1800's. Some modern writers have questioned how much white frontiersman really wore buckskin, tanned it themselves or tailored their own clothes --- the argument being that that is a later romanticization and that frontiersmen mostly wore cloth clothing they bought from traders. The frequent diary entries of Lewis & Clark's men tanning hides and making clothes from them clearly refutes this:

July 29, 1805 - Lewis and Clark Journals – LEWIS

…the men have been busily engaged all day in drising [dressing] skins and making them into various garments all are leather dressers and taylors.

 'Dressing' was (and is) a commonly used term for applying oily mixtures to hides and softening them, and the term that Lewis & Clark most often used. The following quote shows that they were dressing the hides with brains, or soap when they ran out of brains:

January 23, 1806 -- At Fort Clatsop -- CLARK
The men of the garrison are Still busily employed in dressing Elk Skins for cloathing, they fine great dificuelty for the want of branes; we have not Soap to Supply the deficiency, nor can we precure ashes to make the lye;

Members of the expedition worked on skins throughout the expedition, but especially during the winter at Fort Clatsop. Brain tan is extremely durable in every use except for moccasin soles, which wear out relatively quickly. Frontiersmen and Indians alike carried extra pairs whenever they traveled:

March 12 1806 – At Fort Clatsop – CLARK

…Our party are now furnished with 358 par of Mockersons exclusive of a good portion of Dressed leather, they are also previded with shirts overalls capes of dressed Elk skins for the homeward journey.

Here are the rest of the tanning and clothing specific quotes that we were able to find in their journals:

September 27, 1804 – Lewis and Clark Journals – CLARK

Capt. Lewis and Some of the party went over to See the Indians Camps  their lodges are 80 in nomber and contain about 10 Souls Each, the most of them women and children. The women are employed dressing buffaloe hides for to make themselves cloathing and to make their lodges &c.

1805 – Snake and Columbia Rivers - ??

…on my return found Great numb. Of the nativs with Capt. Lewis, men all employ[e]d in dressing ther skins mending their clothes and putting their arms in the best order the latter being always a matter of attention with us.

1805 – Great Falls to Three Forks - LEWIS

…I therefore informed the men of my intention, and they put their deer skins in the water in order to prepare them for dressing  tomorrow.

1805 - Whitehouse’s Journal– Joseph Whitehouse

…The natives are light Complectioned decent looking people the most of them well cloathed with Mt. Sheep and other Skins. They have buffalow Robes leather lodges to live in, but have no meat at this time.

April 7, 1805 – Mandan to Yellowstone – LEWIS

…Capt. Clark myself the two Interpretters and the woman and child sleep in a tent fo dressed skins, this tent is in the Indian stile, formed of a number of dressed Buffaloe skins sewed together with sinues.  It is cut in such a manner that when foalded double it forms the quarter of a circle, and is left open at one side here it may be attatched or loosened at pleasure (2u) by strings which are sewed to its sided for the purpose.

May 13, 1805 – Lewis and Clark Journals – LEWIS

…Capt. C. who was on shore the grater part of the day killed several deer and some Elk pricipally for the benefit of theier skins which aree necessary to themn for cloathinf, the Elk skins I now begin to reserve for making the leather boat at the falls.

June 5, 1805 – Whitehouse’s Journal – Joseph Whitehouse

…I Stayed in Camp dressing Skins for to make myself moccasons &c.

June 6, 1805 – Lewis and Clark Journals – LEWIS

…I regretted much being obliged to leave my Elk’s skins. Which I wnted to assist in forming my leather boat; those we had prepared at Fort Mandan being in such a manner that they would not answer.

June 7, 1805 – Lewis and Clark Journals – CLARK

…Cap. Lewis & party did not return this evening. The party has been employed dressing Skins &c.

June 8, 1805 – Whitehouse’s Journal – Joseph Whitehouse

Chapter VIII. From Maria’s River to the Great Falls of the Missouri.

…the men in Camp generally employed Dressing Skins &c.

July 6, 1805 – Whitehouse’s Journal - Joseph Whitehouse

…Some men employed finishing off the Iron boat other dressing Skins &c.

July 6, 1805 – Whitehouse’s Journal

… 2 hunters set out across the river this morning to attempt to kill 1 or 2 Elk for their Zskins. ... I am employed making leather cloaths for the party &c.

July 28, 1805 – Whitehouse’s Journal - Joseph Whitehouse

Chapter XI – From the Three Forks of the Missouri to the Beaver’s Head.

…the men at camp has employed themselves this day in dressing Skins, to make cloathing for themselves. I am employed making the chief part of the cloathing for the party.

July 28, 1805 – Three Forks to Beaver’s Head – CLARK

…Several deer killed to day   men all employed dressing Skins for Clothes & Mockersons,  two men went up the East fork & reports that it is nearly the size of the N. fork, verry rapid & has maney Islands.

July 29, 1805 - Lewis and Clark Journals – LEWIS

…the men have been busily engaged all day in drising [dressing] skins and making them into various garments  all are leather dressers and taylors.

August 11, 1805 – Lewis and Clark Journals – LEWIS

…I instantly supposed that Cruzatte had shot me in mistake for an Elk as I was dressed in brown leather and he cannot see very well.

August 19, 1805 - CLARK

…all hands employed in dressing Skins & Sorting the Indian goods & packing up the baggage.

August 20, 1805 – Whitehouse’s Journal – Joesph Whitehouse

…the men at camp employed dressing Skins &c. the 2 Indians who Stay at Camp behave well their womaen mend & make our moccasons.

August 21, 1805 - Lewis and Clark Journals – LEWIS

Chapter XVI – Searching for Navigable Waters

…The mockersons of both sexes are usually the same and are made of deer Elk or buffaloe skin dresssed without the hair.  Sometimes in the winter they make them of buffaloe skin dressed with the hair on and turn the hair inwards as the Mandans Minetares and most of the nations do who inhabit the buffaloe country.

September 23, 1805 – Lewis and Clark Journals

…these natives live well are verry kind and well dressed in mountain Sheep & deer & Elk skins well dressed, they have buffaloe robes but are verry choice of them.

November,12 1805 – Lewis and Clark Journals - ??

…our party has been wet for 8 days and is truly disagreeable, their robes & leather clothes are rotten from being continually wet, and they are not in a situation to restore them.

November, 15, 1805 – Descending the Columbia – LEWIS

..an if we have cold weather before we can kill & Dress Skins for clothing the bulk of the party will Suffer verry much.

November, 25 1805 – At Fort Clatsop – CLARK

…The Elk being an animal much larger than Deer, easier to Kill, & better meat (in the Winter when pore) and Skins better for the clothes of our party:

November 30, 1805 – At Fort Clatsop – CLARK

…& the men all employed dressing their skins,…

December 1, 1805 - Lewis and Clark Journals – LEWIS

…many of the men are engaged in dressing leather to cloath themselves, their leather cloaths soon become rotton as they are much exposed to the water and frequently wet.

December 1, 1805 - Lewis and Clark Journals – CLARK

…my hunters returned without any thing saw 2 gang of Elk  a disagreeable situation, men all employed in mending their leather clothes, socks & and Dressing some Leather.

December 2, 1805 – At Fort Clatsop – CLARK

…My hunters returned withour an thin having Seen 2 parcels of elk   men all employed to day in mending their leather Clothes, Shoes, & and Dressing leather.

January 9, 1806 - Lewis and Clark Journals – Lewis

…Our men are now very much engaged in dressing Elk and Deer skins for mockersons and cloathing.

January 18, 1806 – At Fort Clatsop – CLARK

…the men are much engaged dressing skins in order to cloath themselves and prepare for our homeward journey.

January 23, 1806 -- At Fort Clatsop -- CLARK
The men of the garrison are Still busily employed in dressing Elk Skins for cloathing, they fine great dificuelty for the want of branes; we have not Soap to Supply the deficiency, nor can we precure ashes to make the lye;

February 23, 1806 – Lewis and Clark Journals – CLARK

…the men have provided themselves verry amply with mockersons & lesther cloathing, much more so indeed than they have ever been since they have been on the voyage.

March 12 1806 – At Fort Clatsop – CLARK

…Our party are now furnished with 358 par of Mockersons exclusive of a good portion of Dressed leather, they are also previded with shirts overalls capoes of dressed Elk skins for the homeward journey.

March 30, 1806 – Lewis and Clark Journals - CLARK

…instead of the tissue of bark worn by the women below, they ware a kind of leather breech clout as before described as worn by the womin at the enterance of Lewis’s river. The width of a common pocket Handkerchief or something smaller and longer. The two corners of this at one of the the narrow ends are confined in front just about the hips; the other side is then brought between their legs, compresssed into a narrow folding bundle is drawn between their legs, compressed into a narrow folding bundle is drawn tight, and the corners a little spred in front tucked at the ends over and around the part first confined about the waist. A small roab which does not reach the waist is their usial and only garment commonly worn besides this just mentioned. When the weather is a little worm the roab is thrown aside, and the latter truss or breachclout consistutes the whole of their apparreal. This is a much more indisant article than the tissue of bark, and bearly covers the mons venus, to which it is drawn so close that the whole Shape is plainly perseived.

April 3, 1806 – The Start for Home – CLARK

…I observe some of the men amoung them who wear a girdle around the waist between which and the body in front they confine a small skin of the mink or polecat which in some measure conceals the parts of generation. They also frequently wear a cap formed of the skin of the deer’s head with the ears left on it, they\have collars of leather wrought with porcupine quills…

July 15, 1806 – Lewis and Clark Journals – CLARK

…the men employed in drying meat, dressing deerskins and preparing for the reception of the canoes.

August 8, 1806 – Lewis and Clark Journals – LEWIS

…the men with me have not had leasure since we left the Wests of the Rocky mountains to dress any skins or make themselves cloaths and most of them are therefore extreemly bare…the men busied themselves in dressing skins and making themselves cloaths.

August 9, 1806 – Lewis’s Exploration – LEWIS

…the men were all engaged dressing skins and making themselves cloathes except R. & J. Fields whom I sent this morning over the river with orders to proceed to the entrance of the White river in surch of Capt. Clark.

August 29, 1806 – Lewis and Clark Journals – CLARK

…the skins of the party which they had been dressing since yesterday being now completely dressed I derected all loose baggage to be put on board the canoes and at 10 A.M. set out and proceeded on passed the White river at 12 oClock and halted below the enterance of Shannons Creek…

September 7, 1806 – Lewis and Clark Journals – LEWIS (Pelecan Island a little above the Petite River de Seenoux.)

…several of the party exchanged leather for linen Shirts and beaver for corse hats.

October 17, 1806 – Lewis and Clark Journals - ?? (speaking of the tribes of the main Columbia river)

… Their garments consists of a short shirt of leather and a roabe of the Skins of Deer or the antilope, but fiew of them ware Shirts all have Short robes.

November 29, 1806 – Lewis and Clark Journals – CLARK

…all the others engaged drying their leather before the fire and prepareing it for use – they having but fiew other Species of Clothing to ware at this time.

August 22, ???? – Lewis and Clark Journals – CLARK

…the men at camp employed dressing their Deer Skins & making their mockasons &c. I am employed making up their leather shirts & overalls.

May 10, ???? – Lewis and Clark Journals – LEWIS

…The Chief had a large conic lodge of leather erected for our reception and a parsel of wook collected and laid at the door after which he invited Capt. C. and myself to make that lodge our home while we remained with him.

1806 - …speaking of the “Chyennes”

Their women are homely, corse feetured wide mouths they ware simpially a leather habit made in a plain form of two pieces of equal length and equal weadth, which is sewn together with sinues from the tail to about half way from the hip to the arm…those dresses usially fall as low as mid leg, they are frequently ornemented with beeds and shells & Elk tuskes of which all Indians are very fond of.

August 21 -  Lewis and Clark Journals - ???

…these leggings are made of the skins of the antelope and the chemise usually of those of the large deer Bighorn and the smallest elk.

…They [Sioux] live in in tents of dressed leather, which they transport by means of horses and dogs, and ramble from place to place during the greater part of the year.

Lewis: River and Creeks (Platte river, Missouri)

…and the savages sometimes descend in small leather canoes made of a Buffaloe’s skin.

Extract from letter to editors of the baltimore Federal Gazette, regarding the returning explorers, under date of St. Louis, September 23, 1806:

…They have the appearanced of Robinson Crusoes – dressed entirely in buckskins.