The coal industry of Maverick County is located along a section of the Olmos Coal Formation immediately north of Eagle Pass. Mining operations developed by Dolch at Dolchburg and by the Olmos Coal, Coke, and Oil Company at Olmos were the largest coal producers in Texas around the turn of the 20th century.
Those photos still fade over time, plastic doesn't prevent the materials from fading or deteriorating. Pencil that's the old lead pencils, or the new graphite pencils will not fade. Graphite is the most stable form of carbon. It's color is grey rather than black, so the line will be lighter than a black color pencil, but they are not susceptible to fading, they are extremely stable.
Today pencils are numbered and/or lettered to tell us how hard the lead is. The higher the number, the harder the lead, and the lighter the markings. However, it wasn't always this way. The earliest pencils were made simply from filling a wood shaft with raw graphite. The hardness of the graphite would differ depending on the quality of the graphite, thus it was different depending on where the pencil was made. The current style of making pencils was developed in 1794 by Nicolas-Jacques Cont (1755-1805).