I know I sound like a fussy old man, but you need to forget most of what you have read/say on YouTube and other internet sites and READ some time tested methodology.
The stickies, and the posts to you and other new makers always suggest using a magnet. Salt, IR thermometers, and such are not good methods. With a magnet and some practice you can nail a HT with a simple carbon steel dead on.
Here is a old post I made on the subjects in issue:
1080 is eutectoid steel - It has the simplest HT. You need to heat it evenly ( avoid overheating the edge) to 1500F and quench as soon as the blade is at that temperature. No need to soak ( hold at austinitization temp) for any length of time. Quench in fast oil, like parks #50,. Water or brine will work, but blades can crack or warp much more likely. Temper twice at 450F. This will give you a hard and tough blade.
Read Kevin Cashen's post in the stickys at the top of the page "Working with three steels". The entire process is explained.
My advise would be to avoid blends of old motor oil and ATF. It will work for many steels, but for shallow hardening steels, it may be less than optimal. Buying a gallon or two of proper quench oil will be a good investment.
1080,1084,1095, W1, W2 all need fast quench oil.
1070 and below often need water or brine to quench them.
O-1, L-6, 5160, S7, and other high alloy steels need a medium speed oil quench.
A-2. D-2,and stainless steels are air quenched, often using quench plates to avoid warping.
You will hear and read a lot of conflicting info about HT procedures. One advantage of 1080/1084 is that most all of those procedures will work for it. The one critical step is the quench. Assuming the steel is about the right temperature, the quench is where the austinite ( what forms above non-magnetic) converts into martensite ( what we want for a knife blade). Cooled too fast...it cracks or warps, cooled too slow...the blade is too soft or only partially hardened. Most blade steels between 1080 and W2 ( from .80% to 1.00% carbon) have only about one second to lower the steel temperature from 1500F to below 900F. That is what the words "fast", "medium", and "slow" mean in quench oil ratings.
As to using a magnet to determine the blade temperature....it is a good system. At about 1300F the steel changes from one structure to another. It looks the same, but the new structure is not magnetic. Checking the steel by using a magnet ( the cheap telescopic pick-up magnets work well) as the blade heats up will tell you when this change occurs. At this point it is not ready to quench ( even though many will tell you to quench then). It has to heat up about 150-200 degrees more. You observe the color at non-magnetic, and heat it up a shade or two brighter. That should put you in the ball park. The things you want to do are keep the blade moving and turning, so the thicker spine and the thinner edge are as near the same temperature as possible. Avoid overheating the edge...that the part you are going to use in cutting.
Once the blade is at the austinitization temperature, quench in a smooth and even plunge into a gallon or more of the proper quenchant. Quench straight in, point first. Only move the blade up and down, or in a cutting motion from spine to edge. Avoid moving it from side to side or it may warp. After about 7-10 seconds, pull the blade out and check it for warps. If it has some warp or twist, immediately straighten them with gloved hands or on a 2X6 with a wooden mallet. You have until the blade cools to 400F to do any straightening. At 400F the steel converts into martensite, and will become very hard and very brittle. Do not attempt to straighten any more. Allow to cool to room temperature, wash off the oil, and as soon as possible , place in the oven at 400-450F to temper for one to two hours. Take out and let cool to room temp and put back in the oven for a second temper cycle. Now your blade is hard and tough.
There is a lot more to HT than this, but that is a basic starter procedure. Again, reading Kevin's posts will provide a lot more detail.
) A thermocouple/digital reader wouldn't give very accurate readings AT ALL in a coal forge, due to the difficulty of obtaining a near perfect uniform heat "across the board".
Sharpening the knife is the very last thing you want to do 99% of the time. If you insist upon sharpening the blade before it is fully polished and the handle is attached, perhaps in order to test the edge-holding, at least dull it again before you start polishing. You will get cut making knives, it is unavoidable, but you can minimize the threat!