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[dpn]

Hi all,

Please forgive this newbie question. If my local lapidary club were open, I'm sure I'd pick up the answer to this question really quickly.

I purchased a slab of bloodstone from eBay with the intent of using is as a photographic background. It's a nice big slab (6-3/4" x 4-5/8" x 1/4") and it looked great in the auction photo:



In person, it's quite dull and uninspiring. I imagine that the seller got it wet before photographing it for the auction, which strikes me as a fair and reasonable practice.

I'd like to know how to polish it to get it looking nice as a photographic background. Something like a satin finish -- not too glossy -- that brings out the texture and colors of the piece.

I first attacked it using 400 grit wet/dry sandpaper by hand. This accomplished very little, if anything. It became obvious to me that this isn't something that I'm going to be able to polish by hand.

I have a 6" bench grinder with several different cloth buffing wheels (sisal, stitched cotton, loose cotton & muslin) and several different polishing compounds (Black, Brown, Blue, Green & Rouge). Would these be suitable for attempting to polish this slab?

Using the information in the sticky at the top of the forum, I see that "Linde A" polishing compound is recommended. I can certainly buy some of this, but I'm wondering how to best use it. I don't think it'd be able to use it on my bench grinder.

I guess fundamentally I'm wondering whether I can polish this slab successfully using a bench grinder, or whether I really need to be looking at a lapidary-specific tool for this.

Thanks in advance for your patience considering my super-newbie question. Again, I'm sure I'd get this information in my local lapidary group's orientation class in normal times.

Cheers,

Dan

[irockhound]

Hiya and a couple things.  It is pretty normal for seller to wet stones when photographing however it is also pretty std practice to say "Photo taken wet" just for reasons like yours.  How did you know that the seller wasn't selling a polished slab?  If you are altering how it is going to look when a buyer takes it out of the box it should be mentioned otherwise it is just false advertising in my opinion.

Now for the slab.  There are people out there that take pride in polishing slabs by hand!  A slow and tedious process but sure, it can be done.  There are a couple great you tube videos I have watched that the gentleman does everything by hand.  You could speed it up I assume by using a vibrating finish sander with wet or dry silicon carbide sheets with keeping the slab paper surface wet, being very careful to not get the sander itself wet.  Maybe a spray bottle, mist the slab and go at it for a short time till it starts to dry and mist again.   Most slabs if cut by a good saw could have the equivalent of a 500 to 600 finish already.  I know there are white and black stone rouge out there but I also thought there was a colored stone rouge.

The following is only if you don't want to invest the time of hand polishing or investing in better equipment:
The last would be the quickest way and if you are only using it as a backdrop and you do want a reflective shine I assume since you are trying to polish it would be to tape the outer edges of the slab making the tape stick up maybe a 1/16 all around or higher and then use a clear casting resin and pour a light coat over the slab as it self levels.  Make sure the slab is clean by using acetone or other cleaner to remove any possible oils.  You can use a hair dryer to lightly heat the resin which frees up any trapped air bubbles ( best also to not mix aggressively introducing air bubbles in the resin to begin with).

[dpn]

Thanks Steve -- I appreciate the advice! Lots to digest.

1. Yes, the seller disclosed that the slab was wet.
2. Yes, it's "smooth" -- I don't know enough to say to what level it has been polished (or cut), but the slab has definitely had some work done.
3. I love the idea of using a clear epoxy to get a permanent "wet" look, but I want to see if I can improve the finish of this piece before I try that.

[irockhound]

Big Caveat, if the slab was not cut by a saw that was true the surface depending on which side can be concave or convex.  If that it the case I wouldn't go near trying to do anything by hand.  The amount of time it takes for even a flat lap to grind down the surfaces just to get to flat is terrible.  Put a metal straight edge across the slab in both directions and make sure it is flat before proceeding!

[R.U. Sirius]

I second the idea of coating instead of polishing. Krylon acrylic spray worked for some of my small slabs that I didn't want to bother polishing.

You could mask of the stone, and coat small area close to the edge to see if it creates the wet look.

[dpn]

Fantastic advice.

Thankfully, the slab is super flat (determined by ruler).

Stupid follow up question: Once I coat it with some Epoxy 330, I can buff that to a high polish right?

[irockhound]

I wasn't thinking 330 but casting resin.  330 will work I suppose and it will take a polish just would be more cautious in the buffing/polishing stage to not end up with low high spots you don't want to heat up one area too much.  330 is much less fluid than casting resin also so not sure how well it will self level over a slab.  Someone else might be more familiar with using 330 on a larger project and the nuances of it.

[R.U. Sirius]

Fantastic advice.

Thankfully, the slab is super flat (determined by ruler).

Stupid follow up question: Once I coat it with some Epoxy 330, I can buff that to a high polish right?

Just a thought - since you will be using this as a background for photography, high gloss may turn out to be a problem due to reflection of the light source. Why limit your choices of angle and type of illumination? Just aim for a matte or semi-gloss finish, with casting resin or a simple spray-on acrylic.

[dpn]

Again, you've got a really good point R.U. Sirius.

The finish of the slab isn't bad -- I'd call it satin already. So, am I asking the wrong question: Should I be figuring out how to enhance the color of the slab instead of getting it to shine? If it's a matter of just applying a spray on acrylic clear coat ... well, that's easy.

[R.U. Sirius]

They say that there's an easy way, and there's the Samurai way. Everything discussed here thus far falls somewhere in between, but here is a heretic thought that falls left of easy: spray the slab with water, and take that perfect-looking photo of it's colours and texture. Print it on a matte or semi-gloss paper. You now have the background you needed for product photography.

[dpn]

That's a fun idea, but even using a nice printer (I use an Epson P600) the backdrop would obviously be a print.

I'm not trying to be obstinate or contrary at all here. I'll totally admit that I bought a slab without knowing what I'd need to do to make it look good in photographs, and that I may have bitten off more than I can chew. Were we not in Covid-land, I would have already joined my local lapidary club and taken their orientation/beginner classes.

If the answer is just that the slab needs to be "wet" to bring out its colors -- no worries, I'll happily try a clear coat or the epoxy recommended. If it needs a huge amount of labor and/or specialized equipment, that's cool too -- I'll shelve this slab until I have a chance to join the local lapidary club and get some basic hands-on education. If it's not feasible to get the slab looking as good as it did in the seller's photographs, then shame on me for not figuring that out in advance of buying it. Thankfully it was only a few bucks!

I am sincerely grateful for the patient help I've received on this forum in this and other threads. Thank you @irockhound and @R.U. Sirius! This is why I've contributed to the forum. I apologize if my questions have been frustrating.

[irockhound]

If you really like the slab and want it for the back drops, I will offer if you send it to me in a small flat rate usps box, I can flat lap it for you and send it back when done.

[dpn]

It looks like the Sacramento Mineralogical Society's lapidary workshop has reopened, but I don't know if they're teaching the required Beginning Lapidary Class yet. I'd prefer to take the class and learn how to do this myself, but I don't want to wait until mid-2021 or whenever they're fully reopened.

Steve, let me contact the club and see what's going on as far as accepting new members and training them to use the club's equipment. If they're still going to be closed indefinitely, I'll accept your offer with gratitude if you let me pay you for your time and supplies.