Post figuring and testing, you should send your mirror for coating. A bare mirror without the coating will reflect only around 4%-5% of light falling on it.
Until few decades ago, all the astronomical mirrors were coated with silver which is highly reflective. It reflects almost 97% of light. However silver tarnishes very quickly and lose its reflectance within a few months
Nowadays almost all the mirrors are coated with Aluminum. The method is to place the mirror in a very high vacuum chamber and then heat the aluminum coils electrically to its melting point which releases the aluminum atoms and bombard the glass to create a very thin (few atoms thick) reflective layer of aluminum metal on the mirror surface.
Though aluminum is slightly less reflective (~87%) than silver, it is preferred because it doesn’t get tarnish over time. The reason for that is pure aluminum reacts with atmospheric oxygen and it forms a transparent layer of Aluminum Oxide (Al2O3) which is a very hard substance. If you already don’t know; natural occurring impure crystals of aluminum oxide are known as Ruby and Sapphire which are the second hardest gemstones after diamond. Also don’t forget that you used Aluminum Oxide abrasives in the fine grinding stages 😉
I sent my mirror for aluminizing to a Bangalore company (see the name of the vendor ATM Supplies, Sites and Links). It costed me around INR 2000/- in year 2020. Prices may vary so always check with your preferred vendor before sending the mirror.
Aluminum coating last long. Some ATMs have reported their mirror coating surviving for more than 15-20 years!
Below are the pics of my 6″, F/8 mirror post aluminizing. As you can see, quality of the coating is perfect!
Some vendors overcoat the mirror with a thin layer of Silicon Monoxide (SiO) or Silicon Dioxide (SiO2). Though not necessary, you can still check with your vendor if that will be done for your mirror.
Some Afterthoughts: With the rising cost of aluminizing, mirror coating has become a bottleneck for amateur telescope makers. Cost rises exponentially with the increasing size of mirror specially for mirrors over 12 inch diameter. In USA, many makers are experimenting with DIY spray silvering kit made by Angel Gilding with good results. If you are interested, please read about it by clicking the below link.
Astro Khan Telescope Making 