trouble with black marble

[Shaddy Dedmore]

Been having a hard time finding good settings with the marble from
http://www.lasersketch.com/
did anyone else get some samples from there?

It comes out kinda grey and 'dotty', where on the normal black marble from my local flooring co, it comes out white and nice. There just isn't the white black contrast like I'm used to seeing. I lowered my power like it suggests on the site, but then I lose detail...
Any hints on getting better quality? I'm pretty sure it's not my photo processing, as I've tried many combo's of dithering and resolution, plus I've used photograv. I can get great results on the normal tile.

I'm in Washington state, (close enough to portland oregon), is there any place I get get good black marble tile? I also don't mind mail order if there's a place out there with good stuff for lasering. Most of the places I called won't let me hand select, and it's a huge "luck of the draw" to get tiles without filled breaks and swirls. I've only found one place that would let me, but he only has a stock of about 15-20.

I've found a small market here and would love to capitolize but can't find the supplies... grrrr

any ideas?

[Michael Wells]

Shaddy,
You might want to check the stone and make sure that you are lasing on marble instead of the absolute black granite that Lasersketch sells. The granite has to be etched at a much lower power setting or you will most definitely loose definition. I have found a few stone dealers selling a granite as black veinless marble, but if you look closely, you can see that the granite has definite granule composition. That is what causes the difference. The BVM should be solid black with little or no flecking.

If you are using the marble and it appears of good quality to start with, I'm not sure what the problem might be. But then you can try some of the West Coast dealers and see if there is a difference at the same settings.
Michael

[mike wallis]

Hi Shaddy,
I recieved a sample from them as well. The first try I made was not even close to resembling the photo. I adjusted the power down significantly and got the photo to at least come out half as good as the marble im use to using. I also use flooring suppliers and get much better detailed results.
I spoke with Lasersketch and they recomended running the laser at 200 DPI. I gave it a shot and they were right, at 200 DPI its much better than 600 DPI, but 200 DPI isn't what I consider a acceptable Resolution for the Photos I want to put on Marble. I also ran some Photos at 300 DPI and 400 DPI and found that the more resolution I ran the more detail went away. I also noticed there Marble can't produce as many shades of grey that the regular flooring Marble can.
Since Marble is a natural materal its very possible that they have just recieved a bad batch.

Mike

[George M. Perzel]

Hi guys;
Are you all using PhotoGrav?
Thanks
George M. Perzel

[mike wallis]

Hi George,
Yes I do use PhotoGrav and get very simular results "Lasering on Lasersketch Marble" than if I were to just process through Photoshop. Now if I use Photograv and laser on the Marble suppliers I usally use I get very good results.
Do you use this paticular Marble, and if you do are you getting better results than us? I would like to be able to have Lasersketch as a supplier because of the variety they have but I need to get the quality of the engraved Photo better.

Thanks for any help
Mike

[George M. Perzel]

Hi Mike;
I just got some samples in and will try it along with a piece of my standard stuff-will let you know.
George

[Glenn Palhof]

Shaddy sometimes moisture is absorbed into the marble which causes poor
quality.we live in florida so i have seen this problem. 200dpi is where we seem
to get best results and adjust the speed. If you don't move the piece you can just
run it again.
glenn palhof kglass.com

[Rodne Gold]

The laser cannot resolve more than 200 dpi physically , so 200 dpi is more than enough resolution , in fact it might even be too much. DPI is actually the wrong term , its PPI (pixels per inch) that the laser actually resolves.
You can look at this from 2 perspectives - a spot size of 0.003" can only possibly resolve 300 discrete dots per inch and 0.003"is pretty good and really only achievable with beam conditioners and short focal point lenses.
Then the other perspective is that a dot does not represent a shade of grey. A laser can only do 2 colours - white (no engraving) and black (the contrasting mark) , so to represent a shade of grey )of one pixel) one needs to space those dots in matrices or cells , Actual resolution is a function of how many cells can be put into an inch.
How a stone lasers is dependant on the stone itself to a certain extent. The laser can do 2 things , either leech colour or actually physically fracture or vaporise the stone.
If it fractures or vaporises , you end up with areas around the spot size that are either burned , over fractured etc and this can lead to poor results. Marble is an aggregate made up of various other components and what these are or the way the aggregate is made up will determine lasering characteristics. The grey or dotty bits might be due to this dot gain or components within the marble that leave residues and dont "burn out".

We far perfer granite for lasering for a few reasons , firstly the low power required doesnt actually "fracture" the granite as violently but also leeches colour for much better contrast , its a far harder stone so chipping and scratching is not an issue , it is also nowhere near as porous as marble so takes colour or wax filling without the staining of adjacent areas and the quality of polish is far better than what can be achieved on marble. It also is generally a stone with the same grain structure/ properties throughout the tile as it is igneous and not an aggregate. Granites like Zimbabwe black are jet black and are very consistent. We get cheap tiles and pieces from monumental masons , kitchen remodlers , tile warehouses etc. Nice thing as well is that it comes in a lot of nice colours too , like dark reds , greens etc etc.
Premium 22mm thick tile with polished edges works out at about $100 per sq meter or about $10 per sq ft. We get our odd shapes cut by waterjet if needed.
I process granite and photos on granite 2 ways , either directly engraved or we apply a polyester vinyl (most mirror vinyls are polyester) and laser it away and blast for much deeper type engraving.