Firing Process of Cream City Brick

I am going to preface this article by saying I am not a chemist; although I do have some chemistry background with my engineering degree. If any chemists read this, I would love to hear from you in the comments section, since I am still trying to understand this process.

Being a potter, and someone who is very interested in the chemical processes that take place in of firing clay and glazes, I wanted to know more about the firing process of cream bricks and why they become a cream color when the clay is red or purple. Most of the information I have found comes from two reports done by the University of Wisconsin in 1902 and 1906. In "The Clays of Wisconsin and their Uses", Dr Heinrich Ries of the UW Geology department describes this process.  I will combine his description with the research I have done on glazes to attempt to describe this process. I still would like to learn more about it.

An important process that takes place in the firing of these bricks is the calcination of calcium carbonate. Calcination is a process that takes place when any carbonate is heated to a certain temperature. Carbon dioxide is driven off, leaving the oxide of the element. This process is most common in the manufacturing of quicklime for concrete, which is the conversion of CaCo2 to CaO, which is why it is named calcination. It is a process that is used in the production of some glaze ingredients, because it results in a more stable end product, where the color or final mass is already known. For calcium, this occurs at around 1600 deg F. When this point is reached in the brick making process, the brick becomes very porous and fragile. According to Ries, it is important in this process to reach a higher temperature, then a chemical reaction takes place between the lime, silica, and alumina, resulting in a complex silicate compound. When this happens, Ries states that the lime destroys the red coloring of the iron. I have not been able to find any more information on this chemical reaction, and hope to investigate it further with several chemists that I work with. Wollastonite is a compound used in ceramic glazes. The formation of it sounds very similar to this process; it is a compound of silica and calcium that contains small amounts of magnesium and iron. It forms when dolomite or limestone are heated to around 2300 deg F, and is white in color.  The bricks are only fired to around 2100 deg F. I am wondering if due to the high amount of flux this clay contains, it is similar to the Wollastonite process, but is happening at a lower temperature. If any chemists out there could weigh in on this, I am very curious to learn more. Above 2000 deg F, calcium becomes a flux and begins to melt the clay. This is desirable for a glaze, but not for a brick. Full vitrication not of the brick is also not ideal. Since vitrified bricks conduct heat well,  they make poor insulators for houses in cold climates.