The preparations for my journey occupied about ten days, during which time I purchased all the necessary materials for making a panorama of the country, by daguerreotype process, over which we had to pass.
 
To make daguerreotypes in the open air, in a temperature varying from freezing point to thirty degrees below zero, requires different manipulation from the processes by which pictures are made in a warm room. My professional friends were all of the opinion that the elements would be against my success. Buffing and coating plates, and mercurializing them, on the summit of the Rocky Mountains, standing at times up to one's middle in snow, with no covering above save the arched vault of heaven, seemed to our city friends one of the impossibilities knowing as they did that iodine will not give out its fumes except at a temperature of 70 to 80 Fahrenheit. I shall not appear egotistical if I say that I encountered many difficulties, but I was well prepared to meet them by having previously acquired a scientific and practical knowledge of the chemicals I used, as well as of the theory of light: a firm determination to succeed also aided me in producing results which, to my knowledge, have never been accomplished under similar circumstances.
 
S.N. Carvalho, 1859, Incidents of travel and adventure in the far West; with Col. Fremont's last expedition across the Rocky Mountains: including three months' residence in Utah, and a perilous trip across the great American desert to the Pacific, (New York : Derby & Jackson), pp. 20-21

Mr. Bomar, proposed to make photographs by the wax process, and several days were consumed in preparing the paper, etc. I was convinced that photographs could not be made by that process as quickly as the occasion required, and told Col. Fremont to have one made from the window of our room, to find out exactly the time. The preparations not being entirely completed, a picture could not be made that day ; but on the next, when we were all in camp, Col. Fremont requested that daguerreotypes and photographs should be made. In half an hour from the time the word was given, my daguerreotype was made ; but the photograph could not be seen until next day, as it had to remain in water all night, which was absolutely necessary to develop it. Query, where was water to be had on the mountains, with a temperature of 20 below zero? To be certain of a result, even if water could be procured, it was necessary by his process, to wait twelve hours, consequently, every time a picture was to be made, the camp must be delayed twelve hours. Col. Fremont finding that he could not see immediate impressions, concluded not to incur the trouble and expense of transporting the apparatus, left it at Westport, together with the photographer. The whole dependence was now on me. Col. Fremont told me if I had the slightest doubts of succeeding, it were better to say so now, and he would cancel the agreement on my part, and pay me for my time, etc.
 
S.N. Carvalho, 1859, Incidents of travel and adventure in the far West; with Col. Fremont's last expedition across the Rocky Mountains: including three months' residence in Utah, and a perilous trip across the great American desert to the Pacific, (New York : Derby & Jackson), pp. 23-24

I was busily engaged making my daguerreotype views of the country, over which I had to travel the next day. On looking through my camera I observed two of our men approaching over a slope, holding between them a blanket filled with something; curious to know what it was, I hailed them, and found they had been gathering "dried buffalo chips," to build a fire with. This material burns like peat, and makes a very hot fire, without much smoke, and keeps the heat a long time; a peculiar smell exhales from it while burning, not at all unpleasant.
 
S.N. Carvalho, 1859, Incidents of travel and adventure in the far West; with Col. Fremont's last expedition across the Rocky Mountains: including three months' residence in Utah, and a perilous trip across the great American desert to the Pacific, (New York : Derby & Jackson), p. 65

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