It is the element put in parentheses in the HUD next to the name of the element of the particle your cursor is pointing to. For example, SPRK (METL) means the particle is a spark with ctype metal. Ctype is used by the game to store information about a particle. For example the Ctype of lava determines what it will freeze into and ctypes of snow and ice determine what they will melt into. Many other elements use Ctype for different things. Using console commands or the prop tool you can modify this property to get interesting results. Life, tmp, and tmp2 are also used to store different data, and people manipulate them to do interesting things.

very good

Necro

exampl:LAVA with a ctype of iron will freeze into iron

Is the an element to alter the ctype of an element? I am trying to make an addition machine with only 1 pixel so that would be very useful.

@Doooom20: You can't do that directly, but you can utilize serilization: a complex, brain-hurting mess that took me 5 hours to understand: Basically, FILT operates on hexadecimal for wavelengths. With proper sensor usage(use the wiki on FILT for more details), you can "read" that wavelength or write a property to it. For instance, To represent a .life value of 65535 in the .ctype of a FILT particle, the .ctype value should be 0x1000FFB. The serilization formula is: ctype = value + 0x10000000. From there, we add 65535: ctype = 65535 + 268435456 = 268501491, and convert to hex: ctype = 0x1000FFFB. The ctype, funnily enough is where the wavelength is stored, in 30 bits each corresponding to a different color: 7 red, 2 cyan, ect. Each binary bit corresponds to one, and should the .tmp not be set, this is automatically  set to the temprature multiplied by 35 i think. Set this to nothing mode (most are binary operations), or tmp 6. Mind you, THIS ONLY WORKS ON PHOT, BRAY, AND BIZR. Use DETC. I'm not sure if you need to set the tmp1 or tmp2, experiment and get back to me please. Thank you!