Some time ago I created a numerical table that lays out all 78 tarot cards in an array that begins with the 22 trump cards and then follows through with the 56 minor cards, Ace through King and Wands through Pentacles.
I devised this table as a way to find the “mid-point” between cards for a custom spread, but I’ve been thinking it could serve as a kind of “house” system for the tarot in the same way the 36 Lenormand houses are derived. Obviously (and thankfully), very few spreads use all 78 cards in the deck, so I would need a method to randomly pin-point a limited number of “house” cards to match the spread I’m using, similar to “movable houses” (aka “mobile homes”) as applied to Lenormand spreads smaller than the Grand Tableau. (You could, of course, just draw the house cards randomly from a second deck, but what I’m proposing is more fun!)
Some form of Random Number Generator device or program would work as long as it could be limited to numbers below 79, and duplicate numbers would have to be disregarded until the correct number of cards is reached. A cruder method would be to take a page from lithomancy and cast an object multiple times onto a 78-card display, using the cards it lands on for the series of houses. A convention would have to be established for deciding which card to choose when the pointer lands “on the line” between cards. I have a triangular stone with one black point that would serve the purpose quite well. Below are images of what this would look like (here it’s pointing to the 5 of Wands). In practice, it might be best to glue an old deck onto a board so the cards don’t slide around when you toss the object onto them; alternatively, you could make a prepared surface by using a piece of poster board like I did for the Lenormand houses (see below).
Next, I would pull the designated “house” cards from a second deck and lay them out in the pattern of the spread I’m going to use. The shuffle and deal of the reading deck would then commence, with the cards for the reading to be placed on top of the house cards. The latter would be read as additional information for interpretation of the former, identical to the way house cards are used in Lenormand. Here is an example 5-card reading showing the result. In retrospect, it might be advisable to box in your layout by putting some kind of “side-boards” on it to bounce the “pointer” object off, allowing a vigorous toss that can cover the whole field via the rebound; otherwise, unless I consciously target a specific zone, I find that it tends to gravitate toward the middle of the layout and give me adjacent cards.
Here the reading cards are the 9 of Cups, the Tower, the 8 of Wands, the Knight of Pentacles and the 6 of Wands. The gist of this series appears to suggest “rapid recovery (8 of Wands and 6 of Wands) from a serious upset to one’s emotional well-being (9 of Cups and Tower) through steadfast dedication to duty (Knight of Pentacles).” The “house” cards add an emphasis of “stay focused (Ace of Swords), keep your feet under you (7 of Wands), be prepared to move decisively (Chariot) while still remaining grounded in reality (10 of Pentacles) and anticipate a return to emotional stability (4 of Cups).” The reading cards show “what” will transpire and the house cards give a sense of “how.” The bottom card could also be considered a kind of “shadow” card revealing underlying motives, with the top card as its outward expression.