How to Force Canon Pixma MX870 to Print Black

I have the MX870, too, and there is definitely a way to do as you want. 🙂
1. Choose the Print command in one of your open applications.

2. In the drop-down list (I can't tell you which one, as they sometimes appear slightly differently in different applications), select Quality & Media.

3. Put a checkmark in the Grayscale Printing box. Your selection will "stick" until you need to change it for some reason.

4. Now, to make it easier to select this in the future, go to the Presets drop-down list and select Save As. Give your selection a name, and you will be able to switch back and forth from Standard to your own preferred method very easily. I have several Presets defined (I use duplex printing a lot) and find them very convenient.

Steve M. wrote:
Do you know exactly how the printer uses the big black tank vs. the smaller one? Was I correct in my initial assumption that the big black tank is used for text?

Yes you were correct. The larger black tank, which uses pigment-based ink, is used for text while the smaller tank, which is dye-based like the other colours, is for images.

Do you know what ink selection the printer will use if we print a page of text (from Word or Text Edit for example) and DO NOT choose Grayscale? Complex questions but I'm just curious and would like to use my printer and ink in the most economical manner!

If you printed the text document from TextEdit then it would only use the pigment black. There was an issue with Word 2004 where some 'fancy' fonts where perceived as images rather than text and consequently the dye black was used. I believe this was resolved with either the newer versions of Canon drivers - the ones made for Snow Leopard - or with Word 2008.

Steve M. wrote:
So for us MX870 users on a Mac, is Grayscale synonymous with Black for all practical purposes? Can we choose Grayscale to force a colored document to be printed with only black ink?

In theory, using the Grayscale setting will print a document containing an image using black only. However I believe there has been several users claiming that this does not occur. In practical terms I believe that the printer uses magenta mixed with black to make gray. So instead of using only black for an image, which would require some form of line screening which inkjets don't typically employ, the use of magenta could be occurring. I think I will have to get back to you on this after some testing because I feel that the operation of the grayscale setting could still use at least one other colour.

Is there a distinction between a text document and an image document and are colors treated differently for these?

A text document would typically contain no image. Yet it is worth noting that some text items, such as bullet points, are graphical and therefore can be treated by the printer as an image. So it is difficult to be completely accurate about what constitutes a text document. But for your home use I think you would get the most yield from your inks if you did employ the grayscale setting as a default.

This is a non-issue. The colored inks cost as much as the black ink. So there is no cost advantage to printing in black except for text, and that is printed with the pigment ink whether you print color or not. There may be a cost disadvantage to printing grayscale if you do not print enough color to keep the cartridges from drying out.

Regarding your comment about ink prices - I get my printer ink from a discount house called Ink4Art. I always get the 6 pack which is cheaper for me as my printer - Epson requires 6 cartridges. The quality of the ink is excellent.

Steve M. wrote:
Maybe what I'd like to know is if there is a way to encourage the use of the black dye cartridge instead of completely using up the big black tank of pigment ink. As you might suppose, I mostly print text and some web pages and very few actual photos.

The black dye tank is used to complement/enhance the three colours. I don't believe there is a way to use it for text output, unless the text had uneven values and was not considered black but purple or gray. Then you would get the black mixing with magenta or cyan - producing what is called registration black.

Another thing to consider is that the PG520 holds more ink than the CLI-521 Black and therefore gives you a better yield (number of pages). So while the pricing is the same as Bruce mentioned, the PG520 would be costing you less per print for text printing compared to what the CLI_521 Black would.