Zinc anodes will turn black during the plating process. You would normally place a zinc anode into a Anode filter bag.

instead of a straight anode, I recommend rolling it into a cylinder around the edge of the bucket.

This is why commercial plating solutions have a myriad of different additives to increase the "throw" of  the solution. That is electroplater jargon for a solutions ability to coat uneven surfaces. Simple solutions usually have a throw of something close to zero, meaning it will coat very unevenly. Definitly not inside corners.
For a home player, it is pretty much impossible to set up a solution just right for a certain piece. That is also the reason why commercial platers refuse to do small batches. Because the solution and the process must be dialed in for each piece. But for us, there is a way around it: Change electrode positioning during coating. First do it like shown here. Then place the anode very close to the uncoated surfaces. Stick it inside the part if necessary and go on plating. 3D printing fixtures can help suppress short circuits.
And one possible misunderstanding that I pick up: Increasing the voltage and amperage INCREASES Faraday shielding of inside corners. It makes it MORE uneven. Lower voltage improves the throw. You cannot go down to zero, as you have a minimum voltage necessary to drive the process. But going slow and giving it time helps, and might reduce the number of steps required.

As another viewer has noted, the plating process tends to require line of sight between the zinc anode and the areas of the part that you want to be plated. The ideal is have surface of the the zinc anode entirely surrounding and equally distant from all the surfaces of the part. Obviously, it is not practical to achieve that ideal setup, however, if the setup departs too far from that, the process may not work, as was illustrated with the interior of the first part. In the semi-enclosed areas of the part, there will be little electric field to drive the plating process. So, for that somewhat hollow part that wouldn't plate internally, try arranging extra small zinc anode centrally within the hollow space of the part. Given the short distance between that extra anode and the internal surfaces you will have to dial back the current to avoid the fury zinc deposit problem. Good video. Cheers

Watched your and found it interesting I have two helps for   you. One, for plating inside areas, it's best to hang a rolled up sheet of zinc tightly together and locate it to the inside of the part to direct the flow of zinc to the part. Do this step before plating outside surfaces.  Two, after hooking you positive connection, place it into a cotton bucket before you start plating. This will help keep your solution clear of fragments. Again, I enjoyed your video. I too do cars ( 33 /34 Mopar)   Harry B.

Thanks for all the tips! I just reccomend that you focus on the fluid dynamics of your system, since, together with electromagnetic forces (?) it's the advective flow that will carry all the ions to the piece you are plating!!! My best regards!

What a helpful video.  I too have been experimenting with this process and have arrived at almost the same process from watching others -- but you've answered so many of my questions with some simple facts and helpful parts to buy to make my process better.

I didn't use a power supply like yours here -- I used a computer power supply with 12 and 5v outputs -- connected the 5V leads to my donor zinc and had the same exact blackening situation happen -- but great results plating a bunch of bolts.  

It's really satisfying work I've found.  For your own car project, it's a real game changer.

Thanks for sharing everything, subscribing.

Skip the pump and get a aquarium air pump insted. Works just fine. And for zink you can buy zinkanodes for boats and use them

As always, a great video. The best content providers as yourself, show the Good, The Bad, and the Ugly. I will be watching the comments to see the input from your viewers. Thank you for all of time you take to provide us Neophytes.

Thanks for posting both your successes and failures. Very educational video. Thanks for the information and links.

As noted below the electroplating process is directional. The zinc moves from the anode to the part. One solution is to use a bubbler to disturb the path of the zinc. Another solution is to rotate the part while it is electroplating. And another solution is to have multiple anodes around the tank. The effectiveness of these solutions depends on the geometry of the part. For complex parts it might be better to use the brush plating technique. Increasing the current causes the zinc ions to pile up and spread out, which also helps to disperse the path a little, but it is not the best way to evenly plate as it creates dendrites.

I watched another video and the guy put the same amount of suger as salt into the brine, this apparently stops the bild up on the edges. good video cheers.

Try putting a filter around the zinc anoide to help stop the crux bits, maybe a coffee filler. I have no experience in plating but going to give it a go. Keep up the good work.

Regular salt might create chlorine gas because it's NaCl; epsom salt won't because it's MgSO4•7H2O (magnesium sulfate heptahydrate)

in the alkaline zinc plating process, DOHENYS FLOCCULENT can be used to shine the zinc plating and after the passivation process, get that iridescent appearance. Could you test if it also works for acid zinc plating? Unfortunately here in Brazil they use aluminum in similar products and I believe that aluminum will affect the cleaning of the solution. Look for the "DIY Bright Zinc Plating" video to see the amount of flocculant.

Run a small zinc anode inside the component. With this supplying zinc to the inside and the external anodes directing zinc to  the outside, the plating will be more even.

I'm starting to dabble in zinc plating myself, restoring a few rare parts. Thanks for sharing.

Excellent presentation, information, well done sir

The deposition will happen on the closest surfaces to the anode.  Another thing you could try is to use wax on the surfaces already coated, that will make the zinc only have opportunity to stick to the parts that remain in electrical contact.  If you are heating the solution the wax may melt; you might want to turn that off for the second part.

Another solution is to place the sacrificial anode inside the part, that way the zinc will migrate first to the uncoated metal.  Make sure you use something to isolate the cathode from the part.

For a more even plate you need to add a surfactant,  preferably laurel sulphate and use an anode bag to protect your part from zinc particulates.