Borax vs Bicarbonate of Soda: Who Wins To Make Your Laser Burns Darker?

by Alban Bredou

Being very lucky and very spoiled, I have a number of CNC machines and lasers, starting from the 3018-Pro with 5.5W laser. Then, up to the 6550 with a 15W and later 40W, to my weapon of choice right now: The Mandrill with 40W laser

 – although I have just built my brand new YoraHome CNC Laser Engraving Machine 6550-Pro (All-In-One System) with its 80W diode laser.

So, that may take over laser wise and I’ll leave the Mandrill for engraving. 

Throughout my trials and general "having a go test, trying to get the perfect burn has been the aim.

Some people like the sepia brown style burn, others want their burns to look as dark as possible and the debate over what to use to make laser engraving appear darker has raged on.

Using Borax or Bicarbonate of Soda? If so, what proportions, how to put it on, how long to leave it on, does it actually make any difference, or are there any other options out there?

The time has come for me to try to answer at least some of those questions.

Testing Time

A while ago I did some testing on preparing slate to laser engrave, What You Need To Know About Laser Engraving On Slate  and since that had turned out well, I thought I’d use the same template again, only this time I was going to use Lightburn, meaning I could differentiate burn styles between the line shapes, the text and the image.

Template for laser test

 First thing first, I needed to divide up the board into equal sections.

Board in sections for testing

 

Smoothing the board and using painters' tape

Once divided, I could then use my little orbital sander to smooth 3 sections of the board and then cover with painters’ tape 3 areas. 

Board with painters tape

 

Bicarbonate of Soda

Having divided up and masked the board I could start by putting the bicarbonate of soda solution on one section.

After reading lots of different bits of advice on how much bicarb. to water to use, I settled on 1 teaspoon to 250 ml of hot water.

 

Water & Bicarb mix

 

Once thoroughly mixed, I then used a foam “brush” to apply the solution to the board.

 Applying the test solution

 After a couple of minutes, I wiped off excess liquid with a paper towel.

 Wiping off the excess

I left the board to dry, then re-arranged the painters’ tape to leave the last section.

 

Borax

To apply the borax solution I repeated the same process as before, using the same 1 teaspoon to 250 ml of hot water.

This gave me a board with the following layout:

 

The obvious thing to do was to run exactly the same thing on all 4 sections.

Lightburn test template x 4

The values for power and speed are irrelevant here, it is what the solutions did or did not do that I was looking at. But in case you are interested I ran the burn at 2000 mm/min at 40% power.

 

Did using Borax or Bicarbonate of Soda make a difference?

Test of Borax and Bicarb

 

Well, it definitely did.

Between un-sanded and sanded, the major difference was in the colour of the wood, not so much on the burn.

The Bicarbonate of Soda solution definitely made the burn appear darker, but also had a yellowing effect on the wood.

The Borax solution made the burn appear darker without altering the colour of the wood. Perhaps this was the magic formula after all.

But, I had read about other options for darkening the burns, so I flipped over the board, sanded the whole board and tried a few more options.

The first variation was very obvious, go over the burn a second time. This was a huge improvement on the single pass.

Making two passes

 

So, what would slowing down do? The second section was done at half speed, so 1000 mm/min at 40% power. 

Yep, big improvement again.

Now, the next variation seems completely counterintuitive I know, the idea is to run slightly out of focus........ I moved the laser 1 mm higher and went back to 2000 mm/min at 40% power.

Hmmm, not very sharp or clear, so not too impressed with that option.

But there was one more thing I’d read about that I really wanted to try – using shoe polish, yes seriously, the type with the foam attachment that you just dab on.

Single pass with shoe polish

 

I read to dab it on, leave for a minute, then clean off with Isopropanol, hahahaha abject fail

Perhaps if the wood was painted or lacquered first it would work, but on sanded wood it stained really badly, there's no shadow on the picture. Admittedly the burn did look darker a bit darker as well.

Is there a magic formula?

In reality, if you want your burns to be darker you have a few basic choices, slow down, do more than 1 pass or use a mild borax solution.

Yes, we come back to the "usual" answer, practise, practise, practise and test first on a piece of scrap material.

Whatever you do, you can be sure that using a YoraHome laser will give you hours of fun and enjoyment and after a bit of practise you will get the level of burn and darkness that you can be happy with.