You can make a lot of gold through Alchemy transmutes from old expansions. I have covered parts of it in my posts on Jewelcrafting Panthers, Vial of the Sands and my daily routine. Especially if your alchemists are transmutation masters. There are a ton of recipes that can be profitable and they can be combined with tradeskills that use the end products to great effect.
There’s a ton of gold in old expansion recipes and a lot of it is fairly uncontested. I sell panthers faster than I can source the necessary gems and Living Steel.
I’ll be going through the relevant recipes, but first things first.
Alchemy has 3 specializations: Transmutations, potions and elixirs. These give you a bonus when crafting recipes in the corresponding category. For transmutation the bonus averages out to 20% extra yields from all recipes that are affected. The transmutation master effect is active for all recipes from Mists of Pandaria or earlier expansions. It is not active for Warlords of Draenor or Legion recipes.
This means that you will get 0.2 items extra per recipe, which is great! This is pretty massive in markets where you can mass craft as you are guaranteed to get close to the average rate.
Becoming a transmutation master requires completing the aptly named quest Transmutation Master. You need to be level 475 in Alchemy for the quest to appear and it requires you to turn in 4 Living Steel. This is a bit of an entry cost. If you only use alchemy for the Living Steel Cooldown the investment will on average be paid back after using the daily cool down 20 times.
One way to split the transmutation recipes is to do it based on cooldowns. Some transmutations have a shared daily cooldown that resets with the server. The rest of the recipes do not have any form of cooldown and you can craft as many as your materials allow.
The cool downs
There are only really 2 meaningful cool down recipes in alchemy: Pyrium Bar and Living Steel. In general Living Steel is most likely the superior choice as the market is usually much larger. I do mostly Pyrium to support my Vial of the Sands crafting, but Living Steel is definetly more versatile. You can only do one of these per day, so check to see which is the most profitable one on your server and stick to that one. You want to smooth out the proc RNG, so focusing on one is generally preferable.
There is also a non cool down based recipe for Living Steel which we will cover later.
Burning Crusade only really has one relevant Transmutation: Transmute: Primal Might. Primal Mights are used for a lot of crafted epics. The sell rate for Primal Miights is quite low, but if you can use it to craft some of the epics and they are desirable as transmog that can be a good possibility. The current prices on my server indicate a ridiculous profit margin on the Primals. Some of the recipes are quite rare BoE Recipes, so check through the recipe list on Wowhead and see if any of the items are popular as transmog on your realm and if you have or can get the recipe.
Wrath of the Lich King
Wrath added a ton of transmutes, most of which are completely useless. Most of the recipes are used to turn Eternals into other kinds of eternals, but they are all on the shared cooldown and cannot compete with living steel. The other recipe that is added can be quite profitable however. Transmute: Titanium takes 8 Saronite bars to get 1 Titanium Bar. Titanium has a lot of uses primarily as a reagent for Truesteel bars. If you have a Miner you can just melt them into bars and sell those. The bars are also used for Choppers, and a ton of crafted items that sell well for transmog purposes. I have sold a few of the titansteel weapons myself.
With Transmutation mastery you are looking at a cost per Titanium bar of about 6.7 Saronite Bars. This is usually profitable. If you just want to sell the titanium bars straight up my mining guide includes TSM settings for posting them on the Auction House.
Cataclysm was the first expansion to include gem transmutes. These generally take some herbs and uncommon gems to give you rare gems of the same color. Sadly the Cataclysm gems are not particularily useful so the recipes are not that good. The gems sell slow, and profit margins are non-existent, at least on my server.
The only useful non cool down recipe is Truegold. Truegold takes pyrium bars, and Volatiles. They are primarily used for Vial of the Sands. I have trouble getting enough Truegold currently as Volatile supply has dropped off. It is very necessary to stay vigilant for good deals on Volatiles to use this recipe, but it can be very profitable. Particularily when combined with Pyrium bars as the Daily cool down. My Vial of the Sands post includes material groups and shopping operations for all the vial mats, including the mats for Truegold. So check that out if you want an easy set up.
Mists of Pandaria
This is the gold mine expansion in terms of transmutes. There are a ton of recipes, most of which are very useful. The new alchemy metal bar, Living Steel, is used by a large number of luxury mounts that are very profitable. Both for Panthers and for Engineering mounts. Besides the daily cool down there is a Riddel of Steel recipe that has no cooldown. This recipe replaces three of the Trillium Bars with Spirit of Harmony. Spirit of Harmony prices have been going up lately, so this is less lucrative than the daily cool down, but can be a good source.
In addition to Living steel you can turn 10 Ghost Iron Bars into 1 Trillium bar (1.2 with Transmutation master). This will give you easy access to all the Trillium you would want for Living Steel or for transmog crafting. This is usually the most cost effective way to get Trillium hands down. Trillium sells very well on it’s own and it is used in a large number of recipes that still sell. I suggest going through your Mists recipes to see what you can use it for.
The last group of recipes in Mists are the gem recipes. They take one uncommon gem and one Golden Lotus to craft one rare gem of the same color. The red, blue, green and red gems are usually very profitable. The only source of these gems are these recipes and prospecting. You need 20 of each to craft one of the Jewelcrafting Panthers. These sell very well, and more importantly unevenly. These means that there will usually be too few red gems available (the red version is most popular in my experience). Prospecting gives equal amounts of each color and correcting the imbalance with alchemy can be very profitable. The most important material is the Golden Lotus, so if you want to dive into this make sure you search for them often.
I mostly use these recipes to supply my own crafting. As my sales show I have a very high demand myself for these items and Alchemy is the cheapest way to get them. Even running 3 alchemists with daily cooldown I can not cover my own demand and I need to buy Living steel and Truegold from the AH at times. I strongly suggest looking at these recipes yourself and seeing which you can make a profit with just by selling them on the Auction House.
As always the most important way to profit is to get your materials cheaply, so always be on the look out!